Microinvasive breast cancer: pathological parameters, cancer subtypes distribution, and correlation with axillary lymph nodes invasion. Results of a large single-institution series

BACKGROUND: Microinvasive breast cancer is a rare entity in which an invasive component not exceeding 1 mm is found, mostly in a ductal carcinoma in situ setting. Its diagnosis can be difficult and must rely upon immunohistochemistry markers. Many studies have analyzed pathological characteristics of this cancer to delineate its biological profile and possibly identify risk factors of axillary lymph nodes infiltration, which might be present and therefore clinically relevant. Starting from a relative large number of cases we aimed to analyze pathological data, cancer subtypes distribution, and their correlation to nodal metastasis, comparing our results to the existing recent literature. METHODS: All cases of microinvasive breast cancer were retrieved from institutional database from 1992 to 2014. Pathological parameters were analyzed for entire cohort. Moreover, cases submitted to standardized sentinel node biopsy in a restricted period, 2000-2014, were selected to correlate pathology and cancer subtype to axillary lymph nodes status. RESULTS: 174 cases (1.4 % of operated breast cancers) were evaluated in the larger period, 1992-2014. Neither specific pathological parameters were expressed nor a peculiar cancer subtype was represented. 126 cases were selected for axillary staging analysis. Eighteen cases (14.3 %) had lymph nodes metastasis, 10 ITCs (7.9 %), 3 micrometastases (2.4 %), and 5 macrometastases (4 %). An associated intraductal component of carcinoma over 20 mm in maximum dimension resulted significant at multivariate analysis, but only if including ITCs, while this risk factor was not reproduced for micro- and macrometastases only. CONCLUSIONS: Microinvasive breast cancer does not seem to have specific pathological and biological traits. An associated intraductal component of carcinoma >20 mm in size is a specific risk factor for ITCs nodal metastasis. Its clinical significance is anyway limited and therefore sentinel node biopsy should be performed case by case and not routinely.