Survival outcomes of invasive micropapillary carcinoma of the breast: a SEER population-based study

The prognostic significance of invasive micropapillary carcinoma (IMPC) histology in breast cancer is still debated. Additionally, the relationship between different molecular subtypes and survival outcomes in patients with IMPC and invasive ductal carcinoma (IDC) remains unknown. The objective of this study was to investigate whether breast cancer-specific survival (BCSS) and overall survival (OS) differ between IMPC and IDC across molecular subtypes, to better inform subtype-aware risk stratification and personalized management.

Using the Surveillance, Epidemiology, and End Results (SEER) database to identify breast cancer patients, we retrospectively analyzed 959 IMPC and 174,591 IDC cases diagnosed between 2010 and 2016 with non-metastatic diseases that underwent surgery. We compared long-term outcomes of BCSS and OS.

IMPC had a better BCSS (P=0.04) but showed no significant difference in OS (P=0.09) compared with IDC. In multivariate Cox analysis, IMPC histologic type was an independent favorable prognostic factor for both BCSS [hazard ratio (HR) =0.509, P=0.002] and OS (HR =0.637, P=0.003). After propensity score matching (PSM), IMPC still had a better BCSS (P=0.001); we observed no significant difference in OS (P=0.38). While different molecular subtypes have different impacts on survival outcomes, no significant differences were observed in BCSS and OS between IMPC and IDC in relation to Luminal B, human epidermal growth receptor 2 (HER2)-enriched, and triple-negative subtype. In relation to the Luminal A subtype, IMPC had better BCSS (HR =0.399, P=0.001) and OS (HR =0.508, P=0.001). In the case-control cohort, IMPC had a better BCSS (HR =0.423, P=0.005), while no significant difference was observed in OS (HR =0.767, P=0.22) in Luminal A subtype.

Relative to IDC, IMPC presents better long-term survival outcomes, and the survival benefits are confined to the Luminal A subtype.