Duodenal signet-ring carcinoma arising in pyloric gland adenoma with RN7SL1/MUC6 upregulation and mitochondrial dysregulation: A case report

Abstract

BACKGROUND

Duodenal signet-ring cell carcinoma (SRCC) arising from a pyloric gland adenoma (PGA) is exceedingly rare, and its molecular pathogenesis remains poorly defined.

CASE SUMMARY

We present the case of a 61-year-old man who presented with gastrointestinal hemorrhage; endoscopy revealed a polypoid lesion on the anteroinferior wall of the descending duodenum. Histologic examination showed tightly packed pyloric gland-type tubules with focal transition to SRCC. Immunohistochemical analysis demonstrated diffuse mucin (MUC) 6 expression in the PGA component, while CDX2 and CK20 were negative. In contrast, the SRCC areas exhibited strong MUC5AC positivity, markedly increased proliferative activity, and strong nuclear p53 staining, features that provided clear distinguishment from the p53-negative conventional PGA regions. Next-generation sequencing identified pathogenic variants in RN7SL1 and MUC6, together with altered expression of somatic mitochondrial genes (MT-CO2, MT-CO1, MT-ND1, MT-ND4, and MT-CO3), which may collectively contribute to tumorigenesis.

CONCLUSION

This case broadens the molecular landscape of SRCC arising from PGA and underscores the diagnostic and pathogenetic value of next-generation sequencing in characterizing rare gastrointestinal neoplasms.

Key Words: Duodenal tumor; Pyloric gland-type adenoma; Signet-ring cell carcinoma; Immunohistochemistry; Next-generation sequencing; Case report

Core Tip: We report the first documented case of duodenal signet-ring cell carcinoma arising from a pyloric gland adenoma, characterized by distinctive molecular findings identified through next-generation sequencing. Our data highlight variants in RN7SL1 and MUC6, as well as altered expression of the somatic mitochondrial genes MT-CO2, MT-CO1, MT-ND1, MT-ND4 and MT-CO3, suggesting a novel pathogenic mechanism. This case underscores the value of next-generation sequencing in diagnosing rare gastrointestinal neoplasms and broadens our understanding of signet-ring cell carcinoma development.

INTRODUCTION

Pyloric gland adenoma (PGA) is a rare epithelial neoplasm defined by its pyloric-type glandular differentiation. Although classically described within the gastric corpus, an increasing number of studies have identified PGA in extragastric locations, including the duodenum[1]. The malignant potential of duodenal PGA is not well established, as only isolated cases of progression have been documented[2,3]. In the limited reports available malignant transformation typically produces only superficial or focal areas of adenocarcinoma[4], leaving the full spectrum of its oncogenic behavior incompletely understood.

Small bowel malignancies are rare, accounting for roughly 3.5% of all gastrointestinal cancers. Among these, adenocarcinoma is the most common subtype and most frequently arises in the duodenum[5]. Duodenal signet-ring cell carcinoma (SRCC) represents an exceptionally uncommon variant of primary duodenal adenocarcinoma and is often misinterpreted clinically as a benign ulcerative lesion[6]. Prior work has shown that microsatellite instability (MSI) within the high-grade dysplastic component of duodenal adenomas correlates with progression to invasive adenocarcinoma[7]. In addition, de Bakker et al[8] demonstrated that primary duodenal adenocarcinoma exhibits distinct molecular subgroups, nearly half of which fall into a low category for copy-number aberration (CNA) low, characterized by fewer chromosomal CNAs and significantly better survival outcomes (45.5% 5-year survival rate vs 31.0% in CAN high tumors). Their identification of MSI (21.6%) and specific tumor-stroma patterns provides a framework for molecular stratification and may inform future clinical trials investigating novel therapeutic approaches[8]. Despite these emerging molecular insights, the pathways underlying malignant evolution from PGA to SRCC remain largely undefined. This gap in the knowledge base limits both early diagnostic accuracy and the development of targeted treatments.

Here, we describe a rare case of descending duodenal PGA progressing to SRCC, detailing its histologic features, defining tumor-associated molecular alterations, and offering mechanistic insights that may aid early detection and support future precision-based therapeutic strategies.

CASE PRESENTATION

Chief complaints

A 61-year-old man was admitted to our hospital after presenting with black, tarry stools occurring twice daily, along with nausea and intermittent palpitations.

History of present illness

The patient’s symptoms had persisted for approximately 3 days prior to admission.

History of past illness

The patient’s medical history included a 7-year history of hypertension treated with amlodipine besylate (5 mg daily) and benazepril (10 mg daily). He also reported a 30-year history of daily alcohol use (about 100 mL/day) and chronic tobacco use (20 cigarettes/day). A gastric ulcer had been diagnosed 10 years earlier and managed conservatively, though no subsequent follow-up or detailed medication records were available.

Personal and family history

The patient reported no family history of hereditary conditions, disease clustering, or malignancies in first-degree relatives.

Physical examination

Physical examination on admission revealed no notable abnormalities.

Laboratory examinations

Routine blood tests showed normal levels of all evaluated tumor markers, including alpha-fetoprotein, carcinoembryonic antigen, carbohydrate antigen (CA)-125, and CA19-9.

Imaging examinations

Upper endoscopy was performed to evaluate the source of bleeding. Gastroscopy identified two significant duodenal lesions: A 1.2 cm × 1.5 cm pedunculated adenoma located in the duodenal bulb, and a 2.0 cm irregular, polypoid mass in the descending duodenum with active pulsatile bleeding (Figure 1A). This second lesion, positioned opposite the major papilla, displayed several features of malignancy, including marked surface irregularity and diffuse erythema.

Figure 1 Endoscopic and histologic findings of duodenal tumor. A: Polypoid lesion was found in the descending duodenum, presenting surface irregularity and hemorrhage; B and C: Low-power histology demonstrated closely packed pyloric gland-type tubules lined by a monolayer of cuboidal to low columnar epithelial cells with basally positioned round nuclei; D: High magnification examination revealed focal areas of signet ring cell carcinoma arising within the pyloric gland adenoma.

FINAL DIAGNOSIS

SRCC of the duodenum arising in association with a PGA.

TREATMENT

Gastroscopy revealed two distinct duodenal lesions, both of which were completely removed by endoscopic mucosal resection without complications. The excised specimens were retrieved intact and submitted for histopathological assessment.

Microscopic evaluation of the lesion in the descending duodenum showed tightly clustered pyloric gland-type tubules (Figure 1B) and a single layer lining of cuboidal to low columnar epithelial cells (Figure 1C). Importantly, high-power examination identified discrete foci of malignant transformation exhibiting classic SRCC morphology, tumor cells with abundant intracytoplasmic mucin displacing the nucleus to the cell periphery (Figure 1D). These changes strongly suggested progression from a preexisting adenomatous lesion.

Immunohistochemical staining further clarified this transition. The PGA component demonstrated diffuse mucin (MUC) 6 expression (Figure 2A) and CDX2 and CK20 negativity. Furthermore, these areas were p53-negative and exhibited a low Ki-67 index (about 2%). In contrast, the SRCC areas displayed strong MUC5AC positivity (Figure 2B), a markedly increased Ki-67 index (about 80%) (Figure 2C), and strong nuclear p53 staining (Figure 2D). Together, these histological and immunophenotypic findings support a diagnosis of PGA with focal malignant transformation to SRCC, demonstrating a predominantly gastric phenotype profile.

Figure 2 Immunohistochemical findings. The tumor cells showed strong positivity. A: Mucin-6; B: Mucin-5AC; C: Ki-67; D: P53.

Comprehensive molecular profiling was performed using next-generation sequencing on paired tumor and adjacent normal tissues. Differential gene expression analysis was performed using a fold-change threshold of ≥ 2 together with an adjusted P value ≤ 0.05, which is a commonly used criterion to ensure both biological relevance and statistical significance. Cluster heatmap analysis demonstrated distinct gene expression patterns between tumor and normal samples (Figure 3). A total of 9121 differentially expressed genes were identified, including 5624 upregulated and 3497 downregulated transcripts in tumor tissues compared with normal tissues. Among the most prominently upregulated genes were several potentially pathogenic variants, including RN7SL1, RN7SL5P, MUC6, PGC, and RNU5B-1. In contrast, the downregulated (and consequently dysregulated) genes included multiple somatic mitochondrial genes, including MT-CO2, MT-CO1, MT-ND1, MT-ND4, and MT-CO3 (Table 1). RNA sequencing followed by Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis demonstrated significant activation of pathways in tumor tissue related to cytokine-cytokine receptor interactions, tumor necrosis factor signaling, and thyroid hormone synthesis (Figure 4). Gene Ontology analysis further revealed enrichment for molecular functions such as identical protein binding, calcium ion binding, and protein kinase binding. Enriched cellular components were primarily localized to the cytosol, cytoplasm, and plasma membrane, while biological processes were heavily represented by signal transduction pathways (Figure 5). Following tumor board review and confirmation of invasive SRCC diagnosis, the patient underwent definitive surgical treatment with curative-intent pancreaticoduodenectomy (Whipple procedure). The operation proceeded without intraoperative complications, and final histopathological evaluation of the resection specimen confirmed R0 margins.

Figure 3 Comprehensive molecular characterization of matched tumor and normal tissue by next-generation sequencing. Cluster heatmap of differentially expressed genes. Log10 (fragments per kilobase of transcript sequence per million mapped fragments + 1) values were used for hierarchical clustering. Genes with higher expression appear in yellow, whereas lower expression levels are shown in blue.

Figure 4 Kyoto Encyclopedia of Genes and Genomes pathway analysis. The result revealed significant enrichment in the tumor tissue for key processes such as viral protein-cytokine/receptor interaction, tumor necrosis factor signaling, and thyroid hormone synthesis.

Figure 5 Gene Ontology functional enrichment analysis. The result returns the Gene Ontology terms that are enriched among differentially expressed genes against the genomic background, and thus provides information on how the differentially expressed genes are related to certain biological functions. GO: Gene Ontology.

Table 1 Top five up-regulated and down-regulated differentially expressed genes identified by comparing tumor tissue with matched adjacent normal tissue.

Ref. gene	Chr	FPKM	LogFC	Start	End	Regulation
RN7SL1	14	94314.6	2.21133344022303	49586580	49586878	Up
RN7SL5P	9	22974.06	3.33884426000912	9442060	9442380	Up
MUC6	11	4825.41	1.85533269177306	1012823	1036718	Up
PGC	6	4119.34	1.30674514409015	41736711	41754109	Up
RNU5B-1	15	3756.98	1.03904869573663	65296051	65296166	Up
MT-CO2	MT	4780.26	-2.605230914	7586	8269	Down
MT-CO1	MT	4370.38	-2.551138358	5904	7445	Down
MT-ND1	MT	4170.04	-2.860642759	3307	4262	Down
MT-ND4	MT	3861.51	-3.112439091	10760	12137	Down
MT-CO3	MT	3663.65	-2.559351762	9207	9990	Down

Chr: Chromosome; FC: Fold change; FPKM: Fragments per kilobase of transcript sequence per million mapped fragments; MT: Mitochondrial chromosome; Ref: Reference.

OUTCOME AND FOLLOW-UP

At the 3-year follow-up, which included routine serial cross-sectional imaging, surveillance endoscopy, and tumor marker assessment, the patient shows no evidence of disease recurrence and remains clinically disease-free.

DISCUSSION

PGA is a rare duodenal epithelial neoplasm and occurs far less frequently than conventional intestinal-type adenomas. Reported cases suggest a predilection for older adults (median age of 73.5 years) and a slight female predominance. PGA arises more often in the proximal duodenum and is frequently associated with high-grade dysplasia (average size of 23.1 mm); in published series, the average lesion size is approximately 23 mm, and adenocarcinoma is identified in nearly 18% of cases. Both tumor size and tubulovillous architecture have been strongly associated with increased risk of malignant transformation[9]. Duodenal SRCC, however, is exceedingly rare, representing about 1% of all primary duodenal adenocarcinomas[10]. In a study based upon the Surveillance, Epidemiology, and End Results Program data, patients with SRCC were found to be younger and more likely to present with poor differentiation, advanced tumor stage, and higher rates of lymph node and distant metastases compared with those with conventional adenocarcinoma. Age and tumor stage were identified as independent risk factors for the lymph node metastasis in duodenal SRCC. Despite these aggressive clinicopathological features, however, duodenal SRCC and adenocarcinoma demonstrated comparable long-term survival outcomes; notably, combined surgical resection and chemotherapy was associated with improved prognosis in patients with SRCC[11]. SRCC arising in association with duodenal Brunner’s gland hyperplasia has been previously reported[12]; to the best of our knowledge though, SRCC arising from a PGA of the duodenum has not yet been documented. Similar to previously reported cases, our patient did not exhibit distinctive clinical warning sides and instead presented with nonspecific manifestations related to occult gastrointestinal bleeding[6]. This diagnostic subtlety underscores the challenge of recognizing early malignant transformation in PGA and highlights the value of thorough endoscopic evaluation and histologic correlation.

Histopathological evaluation in this case demonstrated classic features of PGA, characterized by tightly arranged tubular structures lined by a single layer of cuboidal to low columnar epithelial cells with round, basally oriented nuclei. High-magnification review revealed discrete foci of malignant transformation showing transition to SRCC. Immunohistochemical staining further emphasized the distinction between the benign and malignant components. The PGA region exhibited diffuse MUC6 expression, consistent with a pyloric gland differentiation. As reported in prior series, the lesion lacked CDX2 and CK20 expression[2], a pattern recapitulated in our case. In contrast, the SRCC component showed strong and diffuse MUC5AC expression, predominantly in the surface epithelium. The known functionalities of MUC5AC include epithelial protection and lubrication; it has also been implicated in cell growth, carcinogenesis, and metastasis[13]. Therefore, the observed shift toward a MUC5AC-dominant mucin phenotype may be associated with malignant progression. Furthermore, areas with SRCC morphology demonstrated a significantly higher proliferative index and strong nuclear p53 immunoreactivity, sharply distinguishing them from the p53-negative PGA regions. Although PGA was historically regarded as a benign lesion, increasing evidence shows that larger or more complex PGAs frequently harbor dysplasia and may progress to adenocarcinoma, often accompanied by aberrant p53 expression[14]. The strong nuclear p53 positivity confined to SRCC foci in our case suggests that TP53 mutation is a key molecular event in this malignant transition and may serve as a valuable histopathological marker for identifying high-risk lesions.

According to prior studies, the progression of PGA appears to follow a multi-step molecular trajectory. Low-grade dysplasia is typically driven by mutations in APC, KRAS, and GNAS, whereas progression to high-grade dysplasia or adenocarcinoma involves accumulation of additional alterations in genes such as CTNNB1, TP53, CDKN2A, PIK3CA, and EPHA5[15]. This malignant evolution is further associated with MSI in high-grade dysplastic regions and intramucosal carcinomas compared with adenomas[7]. Frequent nuclear β-catenin accumulation and recurrent WNT pathway mutations underscore the central role of WNT signaling in tumor initiation. Moreover, the high frequency and distinct distribution of APC mutations in small bowel adenocarcinomas suggest that the traditional adenoma-carcinoma sequence may contribute only modestly to duodenal carcinogenesis[16]. Our next-generation sequencing analysis identified not only multiple somatic mitochondrial genes' dysregulation but also pathogenic variants, including RN7SL1 and MUC6. RN7SL1, transcribed by RNA polymerase III, encodes the RNA component of the signal recognition particle and contributes to the synthesis and trafficking of transmembrane and secreted proteins. It is broadly expressed across diverse tissues and cell lines[17]. Under physiological conditions, RN7SL1 is bound by SRP9/14; when present in an unshielded state (lacking SRP9/14 binding), it becomes functionally dysregulated. Unshielded RN7SL1 can be released via stromal exosomes and transferred to immune or tumor cells, where it disrupts stoichiometric balance. In immune cells, it triggers inflammatory signaling, whereas in breast cancer cells it activates retinoic-acid-inducible-gene-I, promoting tumor growth, metastasis, and therapy resistance[18]. In parallel, the tumor displayed marked mitochondrial dysfunction characterized by downregulation of key respiratory chain components, including MT-CO1 and MT-CO2 (catalytic core of cytochrome c oxidase/complex IV), MT-ND1 and MT-ND4 (essential subunits of nicotinamide adenine dinucleotide dehydrogenase/complex I), and MT-CO3 (a structural component of cytochrome bc1/complex III). Kyoto Encyclopedia of Genes and Genomes pathway analysis further demonstrated enrichment in pathways involved in cytokine-receptor interactions, tumor necrosis factor signaling, and thyroid hormone synthesis. Complementary Gene Ontology analysis revealed that many enriched gene alterations mapped to proteins localized in the cytosol, cytoplasm, plasma membrane, and Golgi apparatus. Collectively, these molecular findings suggest a potential genetic susceptibility involving RN7SL1 and MUC6 alterations and mitochondrial dysfunction that may predispose to PGA formation and progression to duodenal SRCC.

A multicenter retrospective study by Xiao et al[19] demonstrated that radical surgical resection significantly improves overall survival in patients with duodenal adenocarcinoma. Complementing these findings, a National Cancer Database study of 2956 operable cases (2006-2015) reported that patients receiving systemic therapy had markedly better survival than those threated with surgery alone (49 months vs 40 months). Outcomes were comparable between neoadjuvant (8%) and adjuvant (45%) treatment strategies, emphasizing that guideline-supported systemic therapy remains underutilized despite clear survival benefits[20]. Additional evidence was obtained from 3 cases of locally advanced MSI-high duodenal adenocarcinoma achieving pathological complete responses after 2-6 cycles of neoadjuvant pembrolizumab, described by Bouziane et al[21] and highlighting the growing role of programmed cell death-1 blockade in selected patients. Therapeutic advances have also been reported in SRCC of the upper gastrointestinal tract. A randomized study of 85 patients with advanced gastric SRCC found that combination therapy with oxaliplatin, 5-fluorouracil, and paclitaxel significantly improved median survival (11.7 months vs control) and achieved an objective response rate (32.5%). Serum carcinoembryonic antigen, CA19-9, and albumin levels were identified as useful predictive biomarkers in this setting[22]. In our case, tumor board evaluation confirmed invasive SRCC arising from PGA. The patient subsequently underwent curative-intent pancreaticoduodenectomy (Whipple procedure). At 3 years post-operatively, supported by serial imaging, endoscopic surveillance, and tumor marker monitoring, the patient remains without evidence of disease recurrence.

A major limitation of the present study is that the proposed RN7SL1-related mechanism remains speculative and hypothesis-generating, as its functional role has not been established in SRCC. Immunohistochemical analysis demonstrated expression of MUC5AC and p53 in the SRCC component, whereas NGS revealed high expression of RN7SL1 and MUC6. Given that MUC6 is characteristically associated with pyloric gland differentiation, these findings suggest a possible origin from a PGA-like precursor with subsequent phenotypic shift during malignant transformation to SRCC. The discordance between immunophenotypic and molecular profiles may reflect dynamic lineage plasticity during tumor progression rather than a single dominant oncogenic driver. In addition, our observed enrichment of the thyroid hormone synthesis pathway should be interpreted with caution, as it may reflect gene-set overlap among mitochondrial and metabolism-related genes rather than a thyroid-specific biological process. Thyroid hormone-related genes are known to participate broadly in cellular metabolic regulation, which could indirectly relate to tumor metabolism; however, this association remains speculative and was not a primary conclusion of the present study.

CONCLUSION

Despite these limitations, these comprehensive clinicopathologic and molecular analyses provide novel insights into the molecular events underlying PGA-to-SRCC progression. The findings highlight the potential role of phenotypic plasticity during malignant transformation and underscore critical knowledge gaps that warrant further functional and mechanistic studies to improve our understanding and clinical management of this rare and aggressive malignancy.

ACKNOWLEDGEMENTS

The authors would like to thank Hui-Fang Zhang for her helpful advice on the experimental design.