Clinicopathological Significance of Micropapillary Pattern in Lung Adenocarcinoma

The aim of this study was to elucidate the clinicopathological characteristics of the micropapillary (MP) subtype and its correlation with survival in lung adenocarcinoma. We investigated the clinicopathological characteristics, including the incidence, sex, smoking history, tumor size, lymph node metastasis, lymphovascular invasion, distant metastasis, genetic alteration, and prognosis in lung adenocarcinoma with the MP pattern through a meta-analysis. From 48 eligible studies, 19,502 lung adenocarcinomas were included. The incidence rate of the MP pattern was 0.101 [95% confidence interval (CI) 0.075-0.136]. There was no significant difference between stage I and III tumors. Lung adenocarcinoma with the MP pattern showed higher rates of lymphatic invasion (0.526, 95% CI 0.403-0.645). MP pattern was found in 0.150 (95% CI 0.008-0.790) of lung adenocarcinoma with distant metastasis. In lung adenocarcinoma with the MP pattern, the estimated rates of ALK, EGFR, and KRAS mutations were 0.102 (95% CI 0.027-0.322), 0.620 (95% CI 0.444-0.769), and 0.118 (95% CI 0.027-0.393), respectively. The MP pattern of lung adenocarcinoma was significantly correlated with worse overall and disease-free survival rates (hazard ratio 1.704, 95% CI 1.216-2.387, and 2.082, 95% CI 1.541-2.813, respectively). Taken together, identification of the MP pattern in lung adenocarcinoma is useful for prediction of clinicopathological characteristics and prognosis of patients.