The Clinical Impact of Solid and Micropapillary Patterns in Resected Lung Adenocarcinoma.

INTRODUCTION: Since the new adenocarcinoma (ADC) classification was presented in 2011, several authors have reported that patients with solid (S) and/or micropapillary (MP) predominant patterns showed a worse prognosis. On the other hand, there are several patients who have S and/or MP patterns even if their patterns are not predominant. However, the evaluation of these patients is uncertain. METHODS: A total of 531 ADCs were examined. We classified the patients into five subgroups according to the proportion of S and/or MP patterns: (1) both patterns absent (S-/MP-), (2) S predominant (S pre), (3) MP predominant (MP pre), (4) S pattern present although not predominant and MP pattern absent (S+ not pre/MP-), and (5) MP pattern present although not predominant (MP+ not pre). RESULTS: Of the 531 ADCs, 384 (72.3%) were classified as S-/MP-, 55 (10.4%) as S pre, 11 (2.1%) as MP pre, 42 (7.9%) as S+ not pre/MP-, and 39 (7.3%) as MP+ not pre. In a univariate analysis, the recurrence-free survival (RFS) and overall survival differed significantly among the five subgroups (p < 0.01 and p < 0.01, respectively). In a multivariate analysis, patients with S-/MP- had significantly higher RFS rates than did those with other subgroups. On the other hand, patients with MP pre had lower RFS rates than did those with other subgroups. CONCLUSION: Patients with S and/or MP patterns have a poorer prognosis even if their patterns are not predominant. The S and/or MP patterns must be treated at the time of diagnosis.