Breast Microinvasive Carcinoma With Different Morphologies: Analysis of Clinicopathologic Features of 121 Cases

PURPOSE: To investigate the clinicopathological features of patients with breast microinvasive carcinoma (MI). METHODS: The clinical data of 121 cases with breast MI were retrospectively collected. The whole tumor in each case was stained with hematoxylin and eosin (H&E) for pathological evaluation. The relationships among size of tumor, histological grade, tumor-infiltrating lymphocytes (TILs), the number of MIs, type of MI, and lymph node metastasis were analyzed. RESULTS: It was revealed that 86% of the cases had high-grade ductal carcinoma in situ (DCIS) and 63.6% had multiple MIs. The larger size of the tumors, the higher the grade of DCIS, the more the number of MIs; 3.3% of cases had rich TILs (lymphocyte/stroma > 30%) in the DCIS, and 26.5% had rich TILs in MIs. The type A of MIs is characterized by single cells and small clusters of solid cells. Tumor cells in type B of MIs can form glandular ducts. Formal grading of microinvasive is challenging/impossible due to its limited size precluding a representative mitotic count. But nuclear grade and tubule (differentiation) grades can be reported. In addition, 72.7% of cases had type A of MIs and 27.3% of cases had type B of MIs. Type B was found to be highly accompanied by moderate-grade DCIS. Only 6.6% of patients with MI had lymph node metastasis, which was mainly related to MIs with less TILs. CONCLUSION: Breast MI is easy to occur in high-grade DCIS, and multiple infiltration foci may be observed in case with tumor size of higher than 3.5 cm. Microinvasive carcinoma with poor TILs maybe a risk factor for lymph node metastasis in patient with DCIS-Mi.