Objective  We aimed to investigate the clinicopathology and prognosis of invasive micropapillary carcinoma (IMPC) of the breast.

  Methods  This was a single-center retrospective study based on the clinicopathological and follow-up data of 246 patients with IMPC who were treated at the Tianjin Medical University Cancer Institute and Hospital between January 2011 and December 2015. The patients were divided into two groups:we included 143 patients with >50% IMPC in group A and the remaining 103 patients in group B. The cox proportional-hazard regression model, Log-rank test, and Kaplan-Meier method were used for analysis.

  Results  The 5-year disease-free survival (DFS; 76.5% vs. 83.6%, P=0.042) and overall survival (OS; 74.1% vs. 81.6%, P=0.029) of group A were lower than those of group B. The DFS (χ²=5.219, P=0.022) and OS (χ²=3.96, P=0.047) of patients who did not receive radiotherapy in group A were lower than those of patients who received radiotherapy. Multivariate Cox regression analysis showed that HER-2 expression (HR=2.989, 95% CI 1.400-6.384, P=0.005), mammilla invasion (HR=2.388, 95% CI 1.263-4.518, P=0.007), and ≥ 4 lymph node metastasis (HR=2.076, 95% CI 1.080-3.992, P=0.029) were independent risk factors for DFS. Mammilla invasion (HR=1.951, 95% CI 1.054-3.609, P=0.033) was an independent risk factor for OS. The DFS (χ²=6.541, P=0.011) and OS (χ²=6.455, P=0.012) in patients with mammilla invasion who did not receive radiotherapy were significantly lower than those of patients who received radiotherapy.

  Conclusion  As a special type of breast cancer, mammilla invasion indicates a poor prognosis. The prognosis of patients with >50% IMPC was worse than that of patients with ≤ 50% IMPC. Postoperative adjuvant radiotherapy may provide survival benefit to patients with IMPC accounting for 50% or mammilla invasion.