Minor Components of Micropapillary and Solid Subtypes in Lung Adenocarcinoma are Predictors of Lymph Node Metastasis and Poor Prognosis

Lung adenocarcinoma with micropapillary and solid predominant subtypes was reported to be associated with poor prognosis; however, whether minor components (non-predominant) of micropapillary and solid subtypes predict poor prognosis remains unknown. In this study, we investigated the predictive and prognostic value of lymph node metastasis of minor micropapillary and solid components. Specimens of resected tumors of 1244 patients were reclassified to determine the predominant subtype and minor components (> 5 %, but not predominant). Of these specimens, 105 contained a micropapillary component and 210 contained a solid component. The correlation between each subtype and lymph node metastasis was analyzed, and survival analyses were used to determine the association between each subtype and patient survival. Adenocarcinomas harboring micropapillary and/or solid components held higher rates of metastatic lymph node stations (25.2 % vs. 15.6 %, p = 0.002; and 24.0 % vs. 14.9 %, p < 0.001, respectively) and lymph nodes (17.3 % vs. 10.1 %, p = 0.004; and 15.5 % vs. 9.7 %, p = 0.001, respectively). Patients with micropapillary and solid components in their tumors showed a shorter median recurrence-free survival (15.8 vs. 62.8 months, p < 0.001; and 20.8 months vs. not reached, p < 0.001) and overall survival (47.0 months vs. not reached, p < 0.001; and 69.0 months vs. not reached, p < 0.001). Minor components of micropapillary and/or solid subtypes of lung adenocarcinoma are correlated with lymph node metastasis and poor prognosis. Thus, it is beneficial to focus not only on predominant subtypes but also minor components to predict prognoses and make therapeutic strategies more comprehensively.