Microinvasive breast carcinoma carries an excellent prognosis regardless of the tumor characteristics.

The clinical implication of microinvasive breast carcinoma (MIBC), especially when multiple foci are identified, is still not clearly defined. This study is designed to collect clinicopathologic and follow up data on patients with MIBC. Histologic data including invasive breast cancer type, nuclear grade, number of microinvasive foci and lymph node status, as well as associated in situ component histologic and biomarkers parameters were recorded. Clinical follow-up data, such as local recurrence, distant metastasis and survival was also noted. Forty MIBC cases were identified among 1180 invasive breast cancer cases between 1998 and 2012, representing 3.4% of the overall invasive cases. The majority of the cases (28/40) had three or less foci of microinvasion and had high nuclear grade (26/40). The associated carcinoma in situ was also mostly high grade. The biomarker expression for estrogen receptor/human epidermal growth factor receptor 2 (ER/HER2) of the in situ component was heterogeneous. Of the 35 cases with known nodal status, 1 had macrometastasis, 1 had micrometastasis, 3 had isolated tumor cells, and the remaining had negative nodes. In the follow-up period (mean 30 months, median 15 months) none of the patients had recurrence, distant metastasis or died of disease. In conclusion, MIBC represents a small portion of invasive carcinomas. The majority of cases have high nuclear grade and are associated with high grade ductal carcinoma in situ. The latter doesn't show consistent ER/HER2 expression. Overall, the number of microinvasive foci, the extent and biomarker expression of the in situ component do not appear to impact the overall excellent outcome.