[Clinicopathologic features of adenoid cystic carcinoma of breast]

Objective: To investigate the clinicopathologic features and grading of adenoid cystic carcinoma (ACC) of the breast. Methods: Sixteen cases of ACC of the breast were analyzed and graded according to the previous report. Immunohistochemical (IHC) staining was used to detect the immunophenotype, Ki-67 proliferative index and expression of EZH2, and the association with tumor grade and outcome was analyzed. Results: Of the 16 cases, 11 were grade Ⅰ, with the epithelial and myoepithelial cells being arranged into tubular and cribriform structure with no solid component; three were grade Ⅱ, which were composed of mixed tubular, cribriform and solid component (<30%); and two were grade Ⅲ, which showed mainly solid component (>90%) and the tumor cells showed basaloid features with scanty cytoplasm and hyperchromatic nuclei, and mitotic count was>5/10 HPF. Immunophenotypically, the epithelial cells expressed CK7, CK8/18 and CD117; the myoepithelial cells expressed p63 and CK5/6; while the basaloid cells were positive for CK5/6 and CD117.Tubular and cibriform ACC showed low Ki-67 and EZH2 expression, while the two cases of solid variant with basaloid features showed high level of Ki-67 and EZH2 expression. Follow-up data were available in 13 cases with a median follow-up period of 42 months. Lung metastasis occurred after 12 months in one grade Ⅱ case and the patient died of disease after 34 months. Vertebral metastasis occurred after 12 months in one grade Ⅲ case and axillary lymph node metastasis occurred in another grade Ⅲ case. All other patients were free of disease at the end of the follow-up periods. Conclusions: ACC shows morphologic spectrum varying from low to high grade, the latter can may give rise to local and distant metastasis. ACC should not be regarded simply as low malignant potential, and should be graded for optimal treatment.