Population-based comparison of prognostic factors in invasive micropapillary and invasive ductal carcinoma of the breast

Background: Invasive micropapillary carcinoma (IMPC) is a variant of breast carcinoma with a higher propensity for lymph node metastases compared with invasive ductal carcinoma (IDC). Methods: Retrospective analysis of 636 IMPC and 297 735 IDC cases in the Surveillance, Epidemiology and End Results database comparing disease-specific survival (DSS) and overall survival (OS) between IMPC and IDC. Results: A higher percentage of IMPC cases (52.0%) had nodal metastases compared with IDC cases (34.6%). The 5-year DSS and OS for IMPC was 91.8% and 82.9%, respectively compared with 88.6% and 80.5% for IDC, respectively. For both IMPC and IDC, oestrogen-receptor positivity was associated with better survival, while having four or more positive lymph nodes or larger tumour size correlated with worse survival. Radiotherapy provided a survival benefit for both histological types. Conclusions: Despite IMPC's higher propensity for lymph node metastasis, IMPC has DSS and OS that compare favourably with IDC.