Long-term Survival Outcomes of Invasive Micropapillary Carcinoma of the Breast: A Population-based Study

Abstract

Background: Whether or not invasive micropapillary carcinoma(IMPC) histology is an independent prognostic factor for breast cancer remains controversial. Moreover, the relationship between different molecular subtypes and survival outcomes of IMPC and invasive ductal carcinoma (IDC) is still unknown.Methods: Using the SEER database to identify breast cancer patients, we retrospectively analyzed 959 IMPC and 174591 IDC cases diagnosed between 2010-2016 with non-metastatic diseases that underwent surgery. Specifically, we compared long-term outcomes of breast cancer-specific survival (BCSS) and overall survival (OS).Results: Relative to IDC patients, IMPC patients were younger at diagnosis and had more moderate and poorly differentiated tumors (93.2% vs. 78.5%), more T3 and T4 tumors (11.0% vs. 6.9%), a higher percentage of nodal involvement (48.9% vs. 30.9%) and AJCC stage III patients (11.9% vs. 6.9%), and presented a higher proportion of HR positivity (91.2% vs. 82.3%) and HER2 positivity (22.3% vs. 16.9%). IMPC had a better BCSS (P=0.039) but showed no significant difference in OS (P=0.095) compared with IDC. In multivariate Cox analysis, IMPC histologic type was an independent favorable prognostic factor for both BCSS (HR=0.509, P=0.002, 95%CI: 0.335-0.775) and OS (HR=0.637, P=0.003, 95%CI: 0.475-0.854). After the case-control matched analysis using the propensity score matching method, IMPC still had a better BCSS (P=0.001); however, we observed no significant difference in OS (P =0.385). 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, HER2-enriched, and Triple-negative subtypes. However, in relation to the Luminal A subtype, IMPC had better BCSS (HR= 0.399, P=0.001, 95%CI: 0.226−0.703) and OS (HR=0.508, P=0.001, 95%CI: 0.345−0.746). In the case-control cohort, IMPC still had a better BCSS (HR= 0.423, P=0.005, 95%CI: 0.233−0.770), but no significantly difference was observed in OS (HR=0.767, P=0.22, 95%CI: 0.502−1.172) in Luminal A subtype.Conclusion: Relative to IDC, IMPC presents better long-term survival outcomes, and the survival benefits are confined to the Luminal A subtype.