Risk Factors and Prognosis Analysis of Infiltrating Micropapillary Carcinoma of Breast: A Retrospective Study

Background: Invasive micropapillary carcinoma (IMPC) is a rare breast cancer subtype with high invasiveness and lymphovascular/lymph node metastasis. While poor prognosis is reported, long-term survival and roles of molecular subtyping/laboratory markers remain unclear. Methods: We retrospectively analyzed 653 IMPC patients from a Chinese center (as of December 2024). Kaplan-Meier estimated progression-free survival (PFS) and overall survival (OS); Cox regression assessed prognostic factors. Results: Among 653 patients with IMPC, the molecular subtype distribution was as follows: HR+/HER2−, 48.2%; HR+/HER2+, 35.4%; HR−/HER2−, 11.0%; and HR−/HER2+, 5.4%. Most patients had T1– 2 disease and were postmenopausal. The 3-year and 5-year OS rates were 97.42% and 93.73%, respectively, while the 3-year and 5-year PFS rates were 90.66% and 81.20%, respectively. Kaplan–Meier analysis showed significant differences in PFS among molecular subtypes, but not in OS. In multivariable analysis, the HR+/HER2+ subtype and higher total bilirubin were independently associated with better PFS, whereas higher systemic immune-inflammation index and stage IIIB were associated with worse PFS. Poorer OS was independently associated with advanced stage, no surgery, alcohol consumption history, higher systemic immune-inflammation index, menopausal status, and elevated blood glucose, while mastectomy and endocrine therapy were associated with better OS. Conclusion: IMPC shows favorable OS but requires progression risk monitoring. PFS varied by molecular subtype, while OS did not. Molecular typing, clinical stage, and inflammatory/biochemical markers aid prognosis and personalized treatment.