Pattern of metastasis outside tumor-bearing segments in primary lung cancer: Rationale for segmentectomy

Background Patterns of intrapulmonary metastasis, particularly metastasis outside tumor-bearing segments, were investigated in lung cancer patients to address the rationale for segmentectomy. Methods In a consecutive series of patients who underwent resection of two or more pulmonary segments for primary lung cancer, intrapulmonary spread patterns, such as segmental/intersegmental node metastasis and pulmonary parenchymal metastasis, were pathologically examined. Results Eligible 244 lesions included 167 adenocarcinomas, 66 squamous cell carcinomas, and 11 large cell carcinomas. Pathologic stages included 0 to IA (n = 111), IB (n = 56), IIA (n = 31), IIB (n = 20), IIIA (n = 23), and IIIB to IV (n = 3); and N1 (n = 26) and N2 (n = 22). Intrapulmonary spread was observed in 24 cases (9.8%). Of these, metastasis outside tumor-bearing segments was only observed in 4 cases (1.6%), and such cancer spread was more frequently seen in cases with extrapulmonary (hilar to mediastinal) nodal metastasis (7.9%) than in cases without extrapulmonary metastasis (0.5%; p = 0.01). Metastasis outside tumor-bearing segments was not observed in 64 tumors with pure or mixed ground glass opacity features on computed tomography. Although tumor location (peripheral or central/intermediate) was not related to the incidence of metastasis outside tumor-bearing segments, intrapulmonary spread was observed in only 1 of 52 peripheral small (≤20 mm) tumors. Conclusions Metastasis outside tumor-bearing segments is rarely observed in cases with tumors (1) without extrapulmonary nodal metastasis and (2) with ground glass opacity or peripheral small (≤20 mm) features.