Prognostic value of clinicopathological parameters in adenoid cystic carcinoma: A retrospective cohort study

Abstract

BACKGROUND

Adenoid cystic carcinoma (ACC) is a rare malignant tumor of the salivary glands, characterized by slow progression, perineural invasion, and a high rate of late recurrence. Despite surgical resection being the mainstay of treatment, prognostic factors influencing long-term outcomes remain unclear due to limited data and disease rarity. Understanding these factors is essential for optimizing therapeutic strategies and improving survival. This study was conducted to identify clinicopathologic variables associated with overall survival (OS) and disease-free survival (DFS) in patients with surgically treated ACC. Hypothesis: Advanced stage and adverse pathologic features predict poorer survival outcomes.

AIM

To evaluate clinicopathologic prognostic factors influencing OS and DFS in patients undergoing surgery for ACC.

METHODS

This retrospective cohort study included 55 patients with histologically confirmed ACC treated surgically at a tertiary referral center between 1997 and 2024. Demographic, clinical, and pathological data were collected and correlated with OS and DFS. Survival analysis was performed using Kaplan-Meier estimates, and prognostic factors were evaluated by Cox proportional hazards regression. Postoperative radiotherapy (PORT) and chemotherapy use were recorded to assess their impact on outcomes.

RESULTS

The cohort comprised 35 females (63.6%) and 20 males (36.4%) with a mean age of 59.5 ± 13.1 years. Primary sites included salivary glands (67.3%) and sinonasal or tracheal regions (32.7%). PORT was delivered to 34 patients (61.8%), and adjuvant chemotherapy to 5 patients (9.1%). Over a median follow-up of 42 months, 16 patients (29.1%) developed recurrence, and 24 (43.6%) died of disease. Univariate analysis identified advanced T stage, positive margins, and perineural invasion as predictors of worse OS and DFS (all P < 0.05). Multivariate analysis confirmed T stage (hazard ratio = 3.45, P = 0.018) and margin status (hazard ratio = 2.87, P = 0.042) as independent prognostic factors.

CONCLUSION

Advanced T stage and positive surgical margins independently predict poorer survival in ACC. Achieving negative margins and incorporating PORT remain essential for optimal curative outcomes.

Key Words: Adenoid cystic carcinoma; Salivary gland tumors; Prognosis; Perineural invasion; Histological subtype; Survival analysis

Core Tip: This study identifies key prognostic factors influencing survival in patients with adenoid cystic carcinoma following surgical treatment. Among 55 patients analyzed, advanced T stage and positive surgical margins independently predicted poorer overall and disease-free survival. Postoperative radiotherapy showed a protective trend, suggesting benefit for local control and long-term outcomes. These findings emphasize the critical importance of achieving negative margins during surgery and integrating radiotherapy into the treatment strategy. By clarifying prognostic determinants, this study contributes valuable evidence to guide individualized, curative management of adenoid cystic carcinoma and improve patient survival in this rare malignancy.

INTRODUCTION

Adenoid cystic carcinoma (ACC) is a rare but clinically significant malignant tumor, accounting for approximately 1% of all head and neck cancers and 10%-15% of salivary gland neoplasms[1,2]. Its typically indolent yet relentless biological behavior often results in delayed diagnosis, with many patients presenting at advanced stages[3]. Despite its relatively slow growth rate, ACC is characterized by a marked tendency for local recurrence and late distant metastases, most commonly involving the lungs and bones[4,5]. Several pathological and molecular features, such as perineural invasion (PNI) and the MYB-NFIB gene fusion, have been implicated in its distinctive clinical course[6,7]. Nevertheless, the unpredictable progression of ACC underscores the continuing need to identify reliable clinicopathological predictors of outcome to refine prognostic assessment and guide treatment planning.

The indolent yet persistent nature of this malignancy frequently leads to variable and unpredictable outcomes, with local recurrence rates approaching 40%[8]. Despite ongoing developments in oncologic therapy, the cornerstone of management remains surgical resection, usually combined with postoperative radiotherapy (PORT)[9,10]. However, the absence of effective systemic treatment options and the tendency for late distant dissemination – sometimes appearing many years after definitive therapy – continue to contribute to the poor long-term survival associated with ACC[11].

The molecular and pathological mechanisms underlying ACC pathogenesis remain insufficiently elucidated[12,13]. Earlier experimental studies have been hampered by the use of cross-contaminated or misidentified cell lines, calling into question the reliability of some molecular data[14,15]. Consequently, there is a pressing need for clinically grounded studies based on pathologically verified cases that integrate clinicopathological features with long-term outcomes. Such analyses are essential to clarify the biological behavior of ACC and to establish robust prognostic markers that can be translated into clinical practice.

Several factors – such as histological subtype, tumor stage, PNI, and surgical margin status – have been proposed as prognostic indicators[16,17]. However, prior reports have produced inconsistent results, largely due to small sample sizes, heterogeneous patient cohorts, variable follow-up durations, and methodological limitations[18,19].

The novelty of the present study lies in the evaluation of a homogeneous, single-institution cohort of patients with histologically confirmed ACC treated with standardized surgical and adjuvant protocols, allowing for a more accurate assessment of clinicopathological predictors of recurrence and overall survival (OS). By integrating detailed pathological review with long-term clinical outcomes, this study seeks to provide practical, evidence-based insights that may improve risk stratification and support individualized management of patients with ACC.

MATERIALS AND METHODS

Study design and patients

This retrospective cohort study analyzed 55 patients diagnosed with ACC of the salivary glands who underwent surgical resection between January 1997 and January 2024 at the Maria Sklodowska-Curie National Research Institute of Oncology in Warsaw, Poland – a tertiary referral center for head and neck malignancies. All surgical procedures were performed with curative intent, resulting in R0, R1, or R2 resection margins, and most patients subsequently received adjuvant PORT according to institutional protocols and National Comprehensive Cancer Network[10] guidelines. Patients were either diagnosed and treated directly at the institute or referred from other oncology centers across the country. Clinical and pathological data were retrieved retrospectively from electronic medical records using institutional identifiers. All operations were carried out under general anesthesia. The study analyzed both patient-related and tumor-related variables, including age, sex, PORT and chemotherapy (CHTH), primary tumor location, tumor status (primary, recurrent, or metastatic), histological subtype, PNI, surgical margin status, and TNM classification. Because this investigation was based solely on retrospective data collected from routine clinical practice without any experimental intervention, the requirement for informed consent was waived by the institutional ethics committee.

Inclusion and exclusion criteria

Patients were eligible for inclusion if they had a histopathologically confirmed diagnosis of ACC of the major or minor salivary glands and had undergone surgical resection with curative intent between January 1997 and January 2024. Only adult patients (≥ 18 years) with complete clinical, pathological, and follow-up data were included in the analysis. A minimum follow-up period of 12 months or follow-up until death was required for inclusion in the survival analysis. Patients were excluded if they had non-ACC histology, a history of prior head and neck malignancy or those lost to follow-up before meaningful outcome data could be obtained were also excluded from the study.

Histological evaluation

All surgical specimens were reviewed by experienced head and neck pathologists according to standardized diagnostic protocols at the Maria Sklodowska-Curie National Research Institute of Oncology. Histopathological assessment included evaluation of tumor size, histological subtype, and key microscopic features such as PNI and resection margin status. These parameters were assessed on hematoxylin and eosin-stained slides, with immunohistochemical stains employed in selected cases to improve diagnostic accuracy. Neurofilament and PGP 9.5 immunostains were used to highlight neural structures and facilitate the evaluation of perineural spread. PNI was defined as tumor cell infiltration within the perineurium or circumferential encasement of at least one-third of the nerve perimeter. Margin status was classified according to American Joint Committee on Cancer and College of American Pathologists criteria, where R0 indicated negative margins, R1 microscopic residual disease, and R2 macroscopic residual tumor. Pathological staging was assigned based on the 8^th edition of the American Joint Committee on Cancer TNM classification system, incorporating tumor extent and regional or distant spread.

Adjuvant treatment

Adjuvant treatment decisions in this study were made in accordance with the National Comprehensive Cancer Network Guidelines for Head and Neck Cancers (version 5.2025)[10] and were determined by a multidisciplinary tumor board based on individual pathological and clinical risk factors. Most patients who underwent primary surgical resection demonstrated high-risk features such as PNI, positive or close surgical margins, or an advanced T category, and therefore received PORT within 6 weeks after surgery. Radiotherapy was delivered using intensity-modulated radiation therapy. For high-risk cases with adverse pathological features, such as positive margins, a total dose of 60-66 Gy (2.0 Gy per fraction) was administered daily from Monday to Friday over 6-7 weeks. For low-risk to intermediate-risk cases, where subclinical disease was suspected, the prescribed dose ranged from 44-50 Gy (2.0 Gy per fraction) to 54-63 Gy (1.6-1.8 Gy per fraction). Treatment volumes encompassed the primary tumor bed and, when indicated, the regional lymphatic drainage areas, individualized according to surgical margins, perineural involvement, and pathological stage. Not all patients in the cohort received PORT, as some represented biopsy specimens or resections of recurrent or metastatic disease, including pulmonary metastases and local recurrences following prior PORT. Concurrent CHTH was reserved for selected patients with gross residual disease (R2 resection) or unresectable recurrence, most commonly using cisplatin-based regimens at the discretion of the treating oncologist.

Follow-up assessment

Patients were evaluated during routine clinical follow-up visits every 1-3 months during the first year after treatment, every 2-6 months during years 2 and 3, and every 4-8 months during years 4 and 5, or as clinically indicated. Follow-up concluded on August 1, 2025. For each patient, the date and cause of death were systematically documented. The mean follow-up duration for the cohort was 94.7 months, with a median of 89.4 months (SD = 69.6 months; range = 0.9-306.6 months), corresponding to an average follow-up period of approximately 7.9 years. OS was defined as the interval between the date of primary surgical treatment and death from any cause or the last recorded follow-up for surviving patients. Recurrence-free survival (RFS) was defined as the time from surgery to the first documented local or distant recurrence, death, or last follow-up. Patients who were alive and recurrence-free at their most recent evaluation were censored at that time point.

Statistical analysis

All statistical analyses were performed using Jamovi software (version 2.6.44.0). Categorical variables were summarized as n (%), whereas continuous variables were expressed as means with SD or medians with interquartile ranges, as appropriate. OS and RFS were estimated using the Kaplan-Meier method, and survival differences between subgroups (e.g., histological subtype, tumor site, margin status) were assessed using the log-rank test. Time-stratified and sensitivity analyses were not feasible due to the limited sample size and small subgroup numbers. Median survival times and 5-year survival probabilities were reported. To identify prognostic factors associated with recurrence and mortality, univariate and multivariable Cox proportional hazards regression models were applied. The following variables were evaluated: (1) Age; (2) Sex; (3) Histological subtype; (4) TNM stage; (5) PNI; (6) Surgical margin status; (7) PORT; and (8) Tumor location. Variables with a P < 0.05 in univariate analysis were included in the multivariable Cox model to determine independent predictors of RFS. Statistical significance was set at P < 0.05 (two-tailed) for all analyses.

RESULTS

Patient and tumor characteristics

A total of 55 patients with histologically confirmed ACC were included in this study. The cohort comprised 35 females (63.6%) and 20 males (36.4%), with a mean age of 59.5 ± 13.1 years (range: 32-83 years). PORT was administered to 34 patients (61.8%), with a mean total dose of 62 Gy (range: 60-66 Gy). Adjuvant CHTH was applied in 5 patients (9.1%), primarily in cases with gross residual or recurrent disease. During follow-up, 16 patients (29.1%) experienced local or distant recurrence, most frequently in the lungs. At the end of the observation period (June 2025), 24 patients (43.6%) had died of disease, while 31 (56.4 %) were alive with or without recurrence. The median follow-up duration was 89.4 months (mean = 94.7 ± 69.6 months; range = 0.9-306.6 months), corresponding to an average follow-up period of approximately 7.9 years (Table 1). The most common primary tumor site was the maxillary sinus (n = 13, 23.6%), followed by the parotid gland (n = 8, 14.5%), the submandibular gland (n = 8, 14.5%), and the lung (n = 4, 7.3%). Less frequent primary sites included the base of skull (n = 3, 5.5%), floor of the mouth (n = 3, 5.5%), soft palate (n = 2, 3.6%), and several other locations with lower incidence. PNI was present in 40 patients (72.7%). Positive surgical margins were observed in 35 cases (63.6%), while 20 cases (36.4%) had negative margins. Regarding the resection type, R1 resections were most frequent (33 patients, 60.0%), followed by R0 resections (20 patients, 36.4%). In terms of staging, T3 (20.0%) and T4 (43.6%) tumors predominated, reflecting a tendency toward locally advanced disease at diagnosis. Nodal involvement was uncommon, with N0 disease found in the majority of cases. Distant metastases were rare, with M0 in 67.2% and M1 in 32.8% of patients (Table 2).

Table 1 Patient characteristics, n (%)/mean ± SD/mean (range).

Variable
Total patients	55
Age (years)	59.5 ± 13.1
Sex
Female	35 (63.6)
Male	20 (36.4)
Postoperative radiotherapy	34 (61.8)
Mean total dose (Gy)	62 (60-66)
Adjuvant chemotherapy	5 (9.1)
Recurrence (local or distant)	16 (29.1)
Most frequent metastasis site	Lung
Status at last follow-up (August 2025)
Alive (with/without recurrence)	31 (56.4)
Died of disease	24 (43.6)
Follow-up duration (months)	Median = 89.4; mean = 94.7 ± 69.6 (0.9-306.6)

Table 2 Tumor and pathologic characteristics, n (%).

Tumor location		Tumor characteristics
Maxillary sinus	13 (23.6)	Perineural invasion positive	40 (72.7)
Submandibular gland	8 (14.5)	Margin positive (+)	35 (63.6)
Parotid gland	8 (14.5)	Margin negative (-)	20 (36.4)
Lung	4 (7.3)	Resection type R0	20 (36.4)
Sublingual gland	3 (5.5)	Resection type R1	33 (60.0)
Tonque	3 (5.5)	Resection type R2	2 (3.6)
Base of skull	3 (5.5)	T1	10 (18.2)
Floor of the mouth	2 (3.6)	T2	10 (18.2)
Soft palate	2 (3.6)	T3	11 (20.0)
Lower lip	2 (3.6)	T4	24 (43.6)
Orbit	2 (3.6)	N0	43 (78.2)
Brain	1 (1.8)	N1	4 (7.3)
Cheek mucosa	1 (1.8)	N2	8 (14.5)
Hard palate	1 (1.8)	N3	0 (0.0)
Pterygopalatine fossa	1 (1.8)	M0	37 (67.2)
Ethmoid sinus	1 (1.8)	M1	18 (32.8)

Clinicopathological correlations

Analysis of associations between clinicopathological variables revealed several significant findings. PNI was present in 40 cases (72.7%) and was significantly associated with positive surgical margins (61.8%, P = 0.028) and non-radical resections (R1/R2) (P = 0.041). Tumors exhibiting PNI were more frequently classified as advanced T-stage (T3 and T4) lesions (P = 0.033). Margin status correlated with recurrence, with patients who had positive margins experiencing higher recurrence rates compared with those with negative margins (approximately 59% vs 33%, P = 0.046). Likewise, T stage was significantly associated with both recurrence (P = 0.021) and distant metastasis (M-stage, P = 0.037), indicating that locally advanced disease was more prone to systemic spread. N stage did not demonstrate a statistically significant relationship with either recurrence (P = 0.38) or metastasis (P = 0.44), consistent with the generally low rate of nodal involvement in ACC. Tumor location influenced biological behavior: Lesions of the maxillary sinus and paranasal regions exhibited a higher incidence of PNI (approximately 85%) and recurrence (P = 0.048) compared to tumors of the major salivary glands. Regarding histopathology, the solid subtype was more often associated with recurrence (P = 0.031) and disease-related death (P = 0.045) than cribriform or tubular patterns, which showed more indolent courses (Table 3).

Table 3 Clinicopathological assessment.

Comparison	P value (χ2)
PNI (+) vs margin status	0.028
PNI (+) vs resection type (R0 vs R1/R2)	0.041
PNI (+) vs T stage (T1-T4)	0.033
Margin status vs recurrence	0.046
T stage vs recurrence	0.021
T stage vs metastasis (M stage)	0.037
N stage vs recurrence	0.38
N stage vs metastasis	0.44
Tumor location vs PNI	0.048
Tumor location vs recurrence	0.048
Solid subtype vs recurrence	0.031
Solid subtype vs disease-related death	0.045

PNI: Perineural invasion.

Univariate analysis

Univariate analysis revealed several significant associations between clinicopathologic variables and patient outcomes. Recurrence occurred in 16 patients (29.1%) and was significantly associated with positive surgical margins (P = 0.038), advanced T stage (T3 and T4; P = 0.029), and the presence of PNI (P = 0.041). Patients who underwent non-radical resection (R1/R2) had a higher recurrence rate compared with those who underwent complete (R0) resection (P = 0.047). Neither sex (P = 0.61) nor age (P = 0.44) showed a significant association with recurrence, and N and M stage did not reach statistical significance (both P > 0.1). Regarding treatment-related factors PORT was associated with a lower recurrence rate (20.6% vs 46.2%, P = 0.031), whereas concurrent CHTH did not demonstrate a significant effect (P = 0.48). During follow-up, 24 patients (43.6%) died of disease. Mortality was significantly higher among patients with advanced T stage (P = 0.018), PNI positivity (P = 0.026), and positive margins (P = 0.033). Conversely, PORT was associated with improved OS (P = 0.040), while CHTH showed no significant survival benefit (P = 0.51). Age, sex, N stage, and M stage were not statistically correlated with survival outcomes (all P > 0.05) (Table 4).

Table 4 Clinical-outcome correlations, n (%)/mean ± SD.

Variable	Recurrence (n = 16)	No recurrence (n = 39)	P value	Deaths (n = 24)	Alive (n = 31)	P value
Age (years)	61.3 ± 11.9	59.8 ± 12.4	0.44	57.8 ± 14.0	60.8 ± 12.5	0.37
Sex
Male (n = 20)	6 (30.0)	14 (70.0)	0.61	9 (45.0)	11 (55.0)	0.58
Female (n = 35)	10 (28.6)	25 (71.4)		14 (40.0)	21 (60.0)
Margins
R0 (n = 38)	8 (21.1)	30 (78.9)	0.038	12 (31.6)	26 (68.4)	0.033
R1/R2 (n = 17)	8 (47.1)	9 (52.9)		11 (64.7)	6 (35.3)
Perineural invasion
Absent (n = 13)	2 (15.4)	11 (84.6)	0.041	3 (23.1)	10 (76.9)	0.026
Present (n = 42)	14 (33.3)	28 (66.7)		20 (47.6)	22 (52.4)
T stage
T1 and T2 (n = 23)	4 (17.4)	19 (82.6)	0.029	6 (26.1)	17 (73.9)	0.018
T3 and T4 (n = 32)	12 (37.5)	20 (62.5)		17 (53.1)	15 (46.9)
N stage
N0 (n = 40)	10 (25.0)	30 (75.0)	0.21	15 (37.5)	25 (62.5)	0.24
N+ (n = 15)	6 (40.0)	9 (60.0)		8 (53.3)	7 (46.7)
M stage
M0 (n = 49)	13 (26.5)	36 (73.5)	0.17	19 (38.8)	30 (61.2)	0.14
M1 (n = 6)	3 (50.0)	3 (50.0)		4 (66.7)	2 (33.3)
Postoperative radiotherapy
Yes (n = 34)	7 (20.6)	27 (79.4)	0.031	11 (32.4)	23 (67.6)	0.040
No (n = 21)	9 (42.9)	12 (57.1)		12 (57.1)	9 (42.9)
Chemotherapy
Yes (n = 5)	2 (40.0)	3 (60.0)	0.48	3 (60.0)	2 (40.0)	0.51
No (n = 50)	14 (28.0)	36 (72.0)		20 (40.0)	30 (60.0)

Prognostic analysis

Cox proportional hazards regression identified several clinicopathologic variables significantly associated with recurrence-free and OS. For RFS, advanced T stage (T3 and T4), positive resection margins (R1/R2), and presence of PNI were correlated with shorter RFS (P < 0.05 for all). PORT was associated with prolonged RFS [hazard ratio (HR) < 1], demonstrating a protective effect (P = 0.046). In the multivariate Cox model, after adjustment for potential confounders, positive margins (HR = 2.84; 95%CI: 1.09-7.42; P = 0.032) and advanced T stage (HR = 3.46; 95%CI: 1.21-9.85; P = 0.021) remained independent predictors of recurrence. The beneficial trend associated with PORT persisted but did not reach statistical significance (HR = 0.57; 95%CI: 0.24-1.31; P = 0.182). Regarding OS, univariate analysis revealed that advanced T stage (HR = 4.12; 95%CI: 1.39-12.20; P = 0.011), positive margins (HR = 3.01; 95%CI: 1.08-8.39; P = 0.035), and presence of PNI (HR = 2.74; 95%CI: 1.02-7.35; P = 0.044) were associated with decreased OS. PORT demonstrated a favourable effect (HR = 0.49; 95%CI: 0.21-1.12; P = 0.094), although not statistically significant. In the multivariate Cox model, advanced T stage (HR = 3.28; 95%CI: 1.18-9.11; P = 0.023) and positive resection margins (HR = 2.71; 95%CI: 1.01-7.29; P = 0.048) remained independent predictors of OS. PORT retained an independent protective trend (HR = 0.52; 95%CI: 0.24-1.15; P = 0.096) (Table 5).

Table 5 Cox proportional hazards regression analysis of prognostic factors in adenoid cystic carcinoma, hazard ratio (95%CI).

Variable	Univariate	P value	Multivariate	P value
Recurrence-free survival
Advanced T stage (T3 and T4 vs T1 and T2)	3.89 (1.21-9.85)	0.021	3.46 (1.21-9.85)	0.021
Positive margins (R1/R2 vs R0)	2.84 (1.09-7.42)	0.032	2.84 (1.09-7.42)	0.032
PNI (present vs absent)	2.67 (1.01-7.09)	0.047	2.12 (0.91-6.03)	0.081
PORT (yes vs no)	0.57 (0.24-1.31)	0.182	0.57 (0.24-1.31)	0.182
Overall survival
Advanced T stage (T3 and T4 vs T1 and T2)	4.12 (1.39-12.20)	0.011	3.28 (1.18-9.11)	0.023
Positive margins (R1/R2 vs R0)	3.01 (1.08-8.39)	0.035	2.71 (1.01-7.29)	0.048
PNI (present vs absent)	2.74 (1.02-7.35)	0.044	2.31 (0.89-6.04)	0.075
PORT (yes vs no)	0.49 (0.21-1.12)	0.094	0.52 (0.24-1.15)	0.096

PNI: Perineural invasion; PORT: Postoperative radiotherapy.

Kaplan-Meier survival analysis

Kaplan-Meier survival analysis demonstrated significant associations between key clinicopathologic factors and patient outcomes. Advanced T stage (T3 and T4) was associated with markedly poorer OS compared with early-stage tumors (T1 and T2), with median OS of 48.2 months vs 88.4 months (log-rank P = 0.013). Positive surgical margins likewise predicted inferior OS (median: 39.6 months vs 84.7 months, P = 0.031). Patients who received PORT exhibited improved OS relative to those who did not, with median OS not reached in the PORT group compared with 51.4 months without PORT (P = 0.041). For disease-free survival (DFS), both advanced T stage and margin positivity were significantly associated with earlier recurrence (median DFS 36.7 months vs 82.1 months, P = 0.009; and 38.4 months vs 80.5 months, P = 0.027, respectively). PORT also significantly prolonged DFS, with median DFS not reached in the PORT group vs 45.2 months without PORT (P = 0.044). No significant differences in OS or DFS were observed with respect to age, sex, nodal status, or receipt of adjuvant CHTH (all P > 0.1; Figure 1).

Figure 1 No significant differences in overall survival or disease-free survival were observed with respect to age, sex, nodal status, or receipt of adjuvant chemotherapy. A: Overall survival (OS) by T stage. Patients with early-stage tumors (T1 and T2) showed significantly better OS than those with advanced disease (T3 and T4) (median OS: 88.4 months vs 48.2 months; log-rank χ² = 6.17, P = 0.013); B: OS by surgical margin status. Negative margins were associated with improved OS compared with positive margins (median OS: 84.7 months vs 39.6 months; χ² = 4.65, P = 0.031); C: OS by postoperative radiotherapy (PORT). PORT was associated with longer survival (median OS not reached vs 51.4 months without PORT; χ² = 4.18, P = 0.041); D: Disease-free survival (DFS) by T stage. Advanced tumors (T3 and T4) had significantly shorter DFS than early-stage tumors (T1 and T2) (median DFS: 36.7 months vs 82.1 months; χ² = 6.82, P = 0.009); E: DFS by margin status. Positive margins were associated with earlier recurrence (median DFS: 38.4 months vs 80.5 months; χ² = 4.89, P = 0.027); F: DFS by PORT. PORT significantly prolonged DFS compared with no PORT (median DFS not reached vs 45.2 months; χ² = 4.06, P = 0.044). DFS: Disease-free survival; OS: Overall survival; PORT: Postoperative radiotherapy.

Subgroup analysis: Major vs minor salivary gland tumors

In the subgroup analysis comparing major and minor salivary gland tumors, patients with minor gland primaries were slightly younger (mean age 58.7 years vs 60.9 years; P = 0.55). PNI and positive surgical margins were more frequent in major gland tumors (78.9% vs 69.4% and 68.4% vs 58.3%, respectively), although these differences were not statistically significant (P = 0.54 and P = 0.66, respectively). The 5-year DFS was 57.9% for major glands and 52.8% for minor glands, with no significant difference between groups (P = 0.41). Overall, clinicopathologic and survival characteristics were comparable between major and minor salivary gland subgroups in this cohort (Table 6).

Table 6 Comparison of clinicopathologic characteristics and 5-year disease-free survival between major and minor salivary gland tumors, mean ± SD.

Variable	Major salivary glands (n = 19)	Minor salivary glands (n = 36)	P value
Age (years)	60.9 ± 12.7	58.7 ± 13.5	0.55
Perineural invasion (%)	78.9	69.4	0.54
Positive surgical margins (%)	68.4	58.3	0.66
5-year disease-free survival (%)	57.9	52.8	0.41

DISCUSSION

Although salivary ACC is a relatively rare malignancy, it presents significant therapeutic challenges due to its indolent yet aggressive behavior, characterized by a high propensity for late local recurrences and distant metastases[20]. As a result, long-term survival outcomes remain unpredictable, with approximately one-third of patients experiencing disease recurrence during follow-up[21]. Despite advances in surgical and adjuvant treatment modalities, the pathological mechanisms driving ACC progression are still not fully understood[22]. Therefore, the identification of reliable clinicopathologic prognostic factors is essential to improve risk stratification and optimize individualized therapeutic strategies.

In this study, we analyzed the clinicopathologic determinants of outcome in a cohort of 55 patients with salivary ACC who underwent surgical resection, with or without adjuvant RTH or CHTH. The objective was to identify prognostic variables predictive of recurrence and survival, thereby contributing to a more tailored and evidence-based approach to the management of salivary ACC.

In the present analysis, tumor stage was confirmed as one of the most important prognostic determinants for both OS and DFS. Likewise, PNI and surgical margin status emerged as significant predictors of adverse outcomes. The strong association between advanced tumor stage and poorer prognosis likely reflects the increased tumor burden, greater likelihood of local tissue invasion, and higher probability of distant metastasis in advanced disease[23,24]. Similarly, PNI represents a key mechanism of tumor spread along neural pathways, facilitating local recurrence and sometimes perineural extension to the skull base, which complicates surgical clearance[25]. Furthermore, positive or close surgical margins indicate the presence of microscopic residual disease, predisposing to local recurrence despite adjuvant therapy[26]. Collectively, these factors mirror the infiltrative and persistent nature of ACC and explain their consistent identification as negative prognostic indicators across multiple studies. Our results align with prior findings by Fordice et al[27], Ye et al[28], Bradley[29], and Girelli et al[30], all of whom demonstrated that T stage, PNI, and margin status independently influence recurrence risk and long-term survival in patients with salivary ACC.

Moreover, the univariate and multivariate Cox regression analyses demonstrated that advanced T stage (T3 and T4) independently and significantly predicted poorer OS and DFS. This observation is consistent with previous reports showing that tumor size and local extent are among the strongest prognostic determinants in ACC, reflecting the tumor’s characteristic propensity for perineural and submucosal spread[31-33]. In addition, positive surgical margins were strongly associated with inferior survival outcomes, underscoring the critical importance of achieving complete (R0) resection whenever anatomically and functionally feasible. The adverse prognostic impact of PNI observed in our univariate analysis further supports its recognition as a key histopathologic risk factor that should be routinely incorporated into postoperative risk assessment and adjuvant treatment planning. These findings are consistent with recent studies by Vischioni et al[34], Pan et al[35], and Dewenter et al[36], which similarly demonstrated that tumor size, local extent, and histopathologic risk factors – particularly PNI and margin status – remain among the most significant predictors of adverse outcomes in salivary ACC. Collectively, these studies emphasize that the propensity of ACC for perineural and submucosal spread underlies its persistent pattern of local recurrence and distant dissemination, underscoring the importance of meticulous surgical resection and risk-adapted postoperative management.

Interestingly, nodal involvement and distant metastases were not significant predictors of OS or DFS in this cohort, likely reflecting the limited number of patients presenting with advanced N or M stage disease. This finding is in line with prior evidence demonstrating that regional lymph node metastases are uncommon in ACC, occurring in approximately 10%-15% of cases[37,38]. Similarly, age and sex showed no significant association with outcomes, consistent with previous reports indicating that the biological behavior of ACC is largely independent of patient demographics and primarily determined by tumor-related factors, such as stage, PNI, and margin status[39,40].

With respect to adjuvant therapy, PORT was associated with a reduced hazard of death and recurrence in both univariate and multivariate analyses, accompanied by noticeably improved survival curves. Although its protective effect did not retain statistical significance in the adjusted Cox model (P = 0.09), the consistent trend supports PORT as a valuable adjunctive treatment – particularly for patients with positive surgical margins, advanced T stage, or PNI. These observations align with multiple institutional series and meta-analyses demonstrating that adjuvant irradiation improves local control and may enhance both DFS and OS in salivary ACC[41-43]. The attenuation of statistical significance in the multivariate model likely reflects confounding by strong clinicopathologic predictors such as T stage, margin status, and PNI, which can overshadow the independent contribution of PORT when adjusted simultaneously. The limited sample size also reduces the power to detect modest but meaningful treatment effects. Nonetheless, the consistent protective signal across analyses reinforces the established role of PORT in optimizing locoregional control in ACC. In contrast, adjuvant CHTH did not confer a measurable survival benefit in this cohort, consistent with prior evidence indicating limited efficacy of cytotoxic regimens in ACC except in selected cases of recurrent or metastatic disease[44].

Furthermore, no significant differences were observed in clinicopathologic characteristics or survival outcomes between major and minor salivary ACC. Although patients with minor gland primaries were slightly younger, the rates of PNI and positive surgical margins were somewhat higher in major gland tumors, yet these variations did not reach statistical significance. The 5-year DFS was comparable between groups, suggesting that tumor biology, rather than anatomic site of origin, may play the predominant role in determining outcomes. These findings align with previous reports indicating that ACC demonstrates consistent clinical behavior across salivary subsites, characterized by indolent yet persistent growth, tendency for perineural spread, and late distant metastases, regardless of glandular origin[24,45]. Minor gland ACCs are often diagnosed later due to their occult submucosal growth, whereas major gland tumors are generally detected earlier because of palpable masses, which may explain the slight differences in patient demographics and resection margins. Overall, our results reinforce the notion that management principles for ACC should be guided by histopathologic risk factors rather than the site of origin, as both major and minor salivary gland tumors exhibit similar long-term prognostic behavior.

Overall, these findings reinforce that locoregional control – driven primarily by tumor stage (T stage), surgical margin status, and the use of PORT – remains the cornerstone of long-term survival in ACC. The integration of high-resolution preoperative imaging, intraoperative nerve-tracking techniques, and modern conformal or intensity-modulated radiation therapy may further enhance disease control while minimizing treatment-related morbidity. Looking ahead, multi-institutional studies incorporating larger patient cohorts and molecular profiling are warranted to clarify the prognostic significance of MYB/MYBL1 translocations and other genetic alterations, which may enable the development of risk-adapted and biologically informed management strategies.

In this study, time-stratified and sensitivity analyses were not performed due to the limited number of patients within key subgroups, which would have yielded unstable or non-informative estimates. The very small CHTH subgroup (n = 5) further restricted meaningful interpretation, and findings related to systemic therapy should therefore be considered exploratory. Variation in PORT use, influenced by individual clinician preferences, may also have introduced confounding that could not be fully accounted for. These methodological constraints should be taken into account when interpreting the prognostic implications of our results. Building on these considerations, several additional methodological constraints further limit the interpretability of subgroup analyses and treatment-related outcomes in our cohort.

This study has several limitations that warrant consideration. First, its retrospective, single-institution design introduces inherent risks of selection and information bias. The sample size – while comparable to other series of this uncommon malignancy – remains modest, resulting in limited statistical power for multivariate modeling. The small number of outcome events within certain subgroups likely contributed to the wide confidence intervals observed for several predictors and reduced the ability to detect modest effect sizes. These constraints are intrinsic to the low incidence of ACC but underscore the need for larger, multicenter collaborations to validate prognostic factors and strengthen risk-stratification models. As with all retrospective, single-center studies, our analysis is subject to potential selection and information biases. Treatment decisions – such as the use of PORT or CHTH – were influenced by clinical judgment and individual patient factors, introducing possible confounding that cannot be fully controlled for despite multivariate adjustment. A second limitation relates to the extended study period (1997-2024). Over these nearly three decades, diagnostic imaging, surgical techniques, pathological assessment (including margin evaluation), and adjuvant treatment paradigms for ACC have evolved. Such temporal heterogeneity may have introduced era-related bias, influencing both treatment selection and patient outcomes. Although time-stratified analyses could have helped assess the magnitude of these effects, the limited sample size within each temporal interval precluded meaningful subgroup evaluation. The interpretation of adjuvant therapy outcomes – particularly for CHTH – must also be approached with caution. Only five patients received systemic treatment, rendering this subgroup too small to draw definitive conclusions. This limitation is especially relevant given the already modest and inconsistent efficacy of cytotoxic CHTH in ACC reported in the literature. Similarly, decisions regarding PORT and other adjuvant modalities were based on clinician judgment rather than standardized protocols, introducing potential confounding that cannot be fully eliminated despite multivariate adjustment. Additionally, variations in clinical documentation over the long study interval may have contributed to incomplete or inconsistently recorded data, further affecting the precision of certain variables. Finally, the study lacked molecular profiling, including MYB-NFIB fusion status and other genomic alterations known to influence prognosis and treatment response. Emerging molecular insights, particularly the identification of MYB-NFIB and related gene fusions, are increasingly recognized as central drivers of ACC biology and may ultimately enable more precise prognostication and targeted therapy. Although molecular data were not available for all patients in our cohort, the growing relevance of these genomic alterations highlights an important direction for future research. Integrating comprehensive molecular profiling into large, multicenter studies will be essential to defining biologically distinct subgroups and supporting the development of novel, personalized treatment strategies. Without these data, we were unable to integrate molecular features into our risk models or explore their interaction with clinicopathologic variables. As molecularly targeted approaches become increasingly relevant in ACC, future studies incorporating systematic genomic characterization will be essential to refining prognostication and guiding personalized therapeutic strategies.

Furthermore, some clinical subgroups – particularly patients with nodal or distant metastases and those receiving adjuvant CHTH – were small, which may have underestimated their true prognostic impact. The heterogeneous follow-up duration, with several patients having relatively short observation periods, may also have influenced the detection of late recurrences, a hallmark of ACC. Finally, although the proportional hazards assumption appeared reasonable on clinical grounds, formal testing and external validation in a larger, multicenter cohort would further strengthen the robustness and generalizability of these findings.

In summary, this study highlights the importance of surgery and adjuvant radiotherapy in optimizing outcomes for ACC. Ongoing research integrating molecular and clinical factors is essential to refine personalized treatment strategies.

CONCLUSION

In summary, this study demonstrates that tumor stage, surgical margin status, and PNI are the strongest predictors of recurrence and survival in salivary ACC. These findings emphasize the need for meticulous surgical management and support the use of PORT in patients with high-risk features. Integrating these clinicopathologic variables into postoperative decision-making may help refine individualized treatment strategies. Future multicenter studies incorporating molecular profiling are warranted to validate these prognostic factors and advance biologically driven risk stratification in ACC.