Extrapulmonary metastases impact survival outcomes of thermal ablation for colorectal lung oligometastases: A multicenter study

Table 1 Demographic and clinical characteristics of patients undergoing image-guided thermal ablation for colorectal lung metastases, mean ± SD/n (%)

Variables		Variables
Age (years)	61.1 ± 9.7	Presence of comorbidities	132 (39.3)
Sex (male)	209 (62.2)	CEA > 20 ng/mL	42 (12.5)
BMI (kg/m2)	20.9 ± 3.6	Extrapulmonary metastasis
Primary tumor location		Liver	70 (20.8)
Rectum	151 (44.9)	Bone	14 (4.2)
Sigmoid colon	68 (20.2)	Abdominal cavity	21 (6.3)
Descending colon	44 (13.1)	Pelvic cavity	18 (5.4)
Transverse colon	21 (6.3)	Other conditions	20 (6.0)
Ascending colon	52 (15.5)	T-stage
Tumor differentiation		T1	12 (3.6)
Poor	24 (7.1)	T2	34 (10.1)
Poor-to-moderate	55 (16.4)	T3	185 (55.1)
Moderate	147 (43.8)	T4	105 (31.3)
Moderate-to-well	70 (20.8)	DFI (< 24 months)	153 (45.5)
Well	40 (11.9)	ITGA therapy timing
Pneumoresection	31 (9.2)	Delayed ablation	111 (33.0)
Synchronous metastases	85 (25.3)	Synchronous ablation	62 (18.5)
CA19-9 > 37 U/mL	47 (14.0)	Upfront ablation	65 (19.3)
Interval between pulmonary resection and IGTA, median (IQR)	19.0 (28.0)	Interval from primary resection to IGTA (< 24 months), median (IQR)	28 (22.0)

IQR: Interquartile range; BMI: Body mass index; CA: Carbohydrate antigen; IGTA: Image-guided thermal ablation; CEA: Carcinoembryonic antigen; DFI: Disease-free interval from primary resection to diagnosis of metastases.

Table 2 Radiological findings for colorectal lung metastases, mean ± SD/n (%)

Variables		Variables
Tumor size (mm)	17.9 ± 10.8	Peridiaphragmatic tumors	30 (8.9)
Tumor size > 3 cm	66 (19.6)	Near parietal pleural
Tumor number		Near mediastinal pleural
1 tumor	135 (40.2)	Peribronchial tumors	52 (15.5)
2 tumors	104 (31.0)	Perivascular tumors	65 (19.3)
3 tumors	71 (21.1)	Emphysema	51 (15.2)
4 tumors	26 (7.7)	CT imaging features
Lung location		Routine features	243 (72.3)
Left lung	131 (39.0)	Air bronchograms	35 (10.4)
Right lung	167 (49.7)	Cavitation, air bubbles, or bullae	37 (11.0)
Bilateral involvement	38 (11.3)
Lung field		Calcifications	12 (3.6)
Central	31 (9.2)	Inflammatory changes	9 (2.7)
Peripheral	297 (88.4)	CT density characteristics
Across multiple field	8 (2.4)	GGO	4 (1.2)
Lung zone		Solid lesions	293 (87.2)
Inner zone	39 (11.6)	Mixed-density lesions	39 (11.6)
Middle zone	72 (21.4)	Near interlobar fissure	106 (31.5)
Outer zone	134 (39.9)	Hilar lymph nodes (+)	46 (13.7)
Across multiple zones	91 (27.1)	Mediastinal lymph nodes (+)	54 (16.1)

CT: Computed tomography; GGO: Ground-glass opacity. Tumor number and distribution (e.g., unilateral vs bilateral, central vs peripheral, lung zones) were recorded to reflect anatomical complexity. Lesions adjacent to critical structures including pleura, vessels, bronchi, and diaphragm were classified due to their potential influence on ablation efficacy. Computed tomography features such as cavitation, air bronchograms, calcification, and lesion density (solid, mixed, or ground-glass opacity) were assessed to describe tumor morphology. Lymph node status was included for its prognostic relevance.

Table 3 Comparison of therapeutic parameters between microwave ablation and radiofrequency ablation, mean ± SD

Parameters	RFA (n = 143)	MWA (n = 193)	P value
Procedure duration (minute), median (IQR)	15.0 (11.0)	7.0 (8.0)	< 0.001
Power output (W), median (IQR)	180 (110)	40 (10)	< 0.001
Temperature (°C)	96.0 ± 8.9	98.9 ± 8.3	0.071
Number of ablation times, median (IQR)	2.0 (2.0)	2.0 (1.5)	0.079
Puncture depth (cm)	7.2 ± 2.2	7.3 ± 2.0	0.784

IQR: Interquartile range; RFA: Radiofrequency ablation; MWA: Microwave ablation. Procedure duration, power output, and ablation temperature reflect key technical distinctions between the two modalities. Microwave ablation typically achieves higher tissue temperatures in shorter timeframes using lower energy settings compared to radiofrequency ablation. Number of ablation times and puncture depth were comparable, suggesting similar procedural complexity across groups.

Table 4 Rates of progression-free survival and overall survival according to the type of extrapulmonary metastasis

	None, % (SE)	Liver, % (SE)	Bone, % (SE)	Abdominal cavity, % (SE)	Pelvic cavity, % (SE)
PFS
1 years	65.4 (0.034)	57.1 (0.059)	49.0 (0.136)	47.6 (0.109)	44.4 (0.117)
3 years	31.0 (0.035)	18.7 (0.048)	16.3 (0.105)	4.8 (0.046)	16.7 (0.088)
5 years	27.3 (0.035)	4.0 (0.037)	0.0	0.0	0.0
OS
1 years	96.4 (0.013)	87.1 (0.040)	64.3 (0.128)	66.7 (0.103)	88.9 (0.074)
3 years	71.0 (0.033)	68.6 (0.055)	21.4 (0.110)	14.3 (0.076)	33.3 (0.111)
5 years	53.0 (0.048)	43.1 (0.085)	0.0	0.0	0.0

OS: Overall survival; PFS: Progression-free survival. This table illustrates the prognostic impact of different extrapulmonary metastasis patterns on survival outcomes in patients undergoing image-guided thermal ablation. Patients without extrapulmonary metastasis demonstrated the most favorable progression-free survival and overall survival across all time points. In contrast, those with bone, abdominal, or pelvic cavity metastases had markedly worse outcomes, with 5-year survival rates approaching 0%. These findings underscore the prognostic importance of metastasis type in risk stratification and treatment planning.

Table 5 Adverse events associated with image-guided thermal ablation for colorectal lung metastases

AEs	Grade	n (%)
Pneumothorax	Overall	169 (50.3)
	A and B	155 (46.1)
	C	12 (3.6)
	D	2 (0.6)
Pleural effusion	Overall	54 (16.1)
	A and B	49 (14.6)
	C	5 (1.5)
	D	0 (0)
Subcutaneous hematoma	A and B	2 (0.6)
Hemothorax	A and B	4 (1.2)
Hemoptysis/blood-streaked sputum	Overall	85 (25.3)
	A and B	82 (24.4)
	C	3 (0.9)
	D	0 (0)
Nausea or vomiting	B	9 (2.7)
Fever	Overall	46 (13.7)
	A and B	44 (13.1)
	C	2 (0.6)
	D	0 (0)
Pneumonia	Overall	5 (1.5)
	C	4 (1.2)
	D	1 (0.3)
Respiratory failure	D	1 (0.3)
Chest pain	Overall	62 (18.5)
	A and B	57 (17.0)
	C	5 (1.5)
	D	0 (0)
Abdominal pain	A and B	6 (1.8)
Skin burn	C	1 (0.3)

AEs: Adverse events. Adverse events (AEs) related to image-guided thermal ablation (IGTA) were recorded according to the Society of Interventional Radiology Clinical Practice Guidelines Classification System[11]. Most AEs were mild and self-limited (grade A and grade B), with pneumothorax being the most common (50.3%), followed by hemoptysis (25.3%), chest pain (18.5%), and fever (13.7%). Major complications (grade C and grade D) were rare, reflecting the overall safety of IGTA.