Negative prognostic influence of micropapillary pattern in stage IA lung adenocarcinoma

OBJECTIVES There is uncertainty as to which factors determine the aggressiveness of lung adenocarcinoma with a micropapillary pattern (MPP). The present study aimed to clarify the influence of a MPP on the malignant aggressiveness of clinical stage IA lung adenocarcinoma. METHODS We retrospectively examined 347 consecutive patients with clinical stage IA lung adenocarcinoma who underwent complete resection. We defined MPP-positive as accounting for ≥5% of the entire tumour. RESULTS Forty-eight (14%) and 299 (86%) patients were MPP-positive and negative, respectively. Lymphatic (P = 0.003) and vessel (P = 0.029) invasion as well as lymph node metastasis (P = 0.002) were more frequent in the MPP-positive than negative group. Five-year disease-free survival (DFS) rates were significantly lower in the MPP-positive than negative group (69.7 vs 89.3%, P < 0.001). Multivariate analysis for DFS showed that MPP (P = 0.048), lymphatic invasion (P = 0.003) and vessel invasion (P = 0.002) were independent poor prognostic factors. In addition, higher proportions (