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 (<5%, 5–30% and ≥30%) of MPP were associated with a poorer prognosis (89.3, 76.0, and 48.1%, respectively; P< 0.001). The prognosis of patients with MPP-positive tumours and negative tumours harbouring lepidic and solid predominant growth patents did not differ (100 vs 96.8%, P= 0.564; 66.7 vs 62.5%, P= 0.791, respectively). On the other hand, the prognosis tended to be poorer for patients with papillary predominant MPP-positive tumours than for those with negative tumours (62.5 vs 82.5%, P= 0.075). CONCLUSIONS: MPP has an effect on tumour malignancy and patients with tumours harbouring a higher ratio of MPP or papillary predominant subtypes have worse survival.