Objective: To study the clinicopathologic features, immunophenotypes and differential diagnoses of invasive carcinoma arising in breast microglandular adenosis (MGACA).
Methods: Clinical and pathologic findings of 3 cases of MGACA were analyzed by histomorphology and immunohistochemical staining of CK7, S-100 protein, ER, PR, HER2, SMA, MSA, p63 and PAS. Literatures were reviewed.
Results: (1) Histologically, 3 tumors all showed a spectrum of glandular proliferations ranging from microglandular adenosis (MGA) to atypical microglandular adenosis (AMGA) to in situ carcinoma (DCIS) to invasive carcinoma. The invasive carcinoma component was ductal in case 1, and matrix-producing in case 2 and case 3. (2) All epithelial cells in MGA, AMGA, DCIS and MGACA were positive for CK7 and S-100 protein, but were negative for ER and HER2. PR was negative in case 1 and case 2 but was low positive in case 3. Myoepithelial cell differentiation was not demonstrated in MGA, AMGA, DCIS and MGACA by immunohistochemical staining for SMA, MSA or p63. PAS staining showed the presence of basement membrane in MGA, AMGA and DCIS, except MGACA.
Conclusions: MGACA is an extremely rare tumor of the breast and has distinct morphological and immunohistochemical features. Further studies are needed to evaluate the clinical behavior of this rare neoplasm.