Factors predicting occult lymph node metastasis in completely resected lung adenocarcinoma of 3 cm or smaller

The aim of the study is to demonstrate the relationship between clinicopathological variables and occult lymph node metastasis in resected lung adenocarcinoma. The clinicopathological characteristics of 471 patients with clinical N2-negative status undergoing resection for lung adenocarcinoma of 3 cm or smaller at Taipei Veterans General Hospital between 2004 and 2012 were retrospectively reviewed. The association between clinicopathological variables and lymph node metastasis was analysed by univariate and multivariate logistic regression. Among the 471 patients, there were 386 (82.0%) patients with pathological N0 status, 35 (7.4%) with pathological N1 status and 50 (10.6%) with pathological N2 status. Greater tumour size (P = 0.002), presence of a micropapillary pattern (P < 0.001), presence of a solid pattern (P < 0.001) and predominant pattern group (micropapillary/solid predominant) (P = 0.001) were significantly associated with higher percentage of occult N2 lymph node metastasis. In multivariate analysis, greater tumour size (P = 0.008), presence of micropapillary pattern (P < 0.001) and presence of solid pattern (P = 0.001) were significant predictors of occult N2 lymph node metastasis in tumours of 3 cm or smaller. When histological pattern was entered as the predominant pattern in multivariate analysis, micropapillary/solid predominant pattern (P = 0.005) was also a significant predictor of occult N2 lymph node metastasis. The presence of micropapillary or solid pattern, as well as micropapillary/solid predominant pattern, is significantly associated with occult N2 lymph node metastasis in lung adenocarcinoma. Radical mediastinal lymph node dissection may help to identify occult lymph node metastasis in these patients.