Primary mucinous cystadenocarcinoma of the breast: a clinicopathologic analysis of one case and review of the literature.

OBJECTIVE: To explore the clinicopathologic features and differential diagnosis of breast primary mucinous cystadenocarcinoma (MCA).

METHODS: Pathological characteristics and immunophenotype of one case of MCA were analyzed. Literature was reviewed.

RESULTS: Grossly, the area of the tumor cut surface was gelationous. Microscopcally, the tumor was composed of variably sized cystic spaces lined by mucus-rich tumor cells with single columnar, stratified appearance and papillary formation. The degree of cytologic atypia varied from region to region. The tumor cells were positive for CK7, GATA3, negative for CK20, ER, PR and HER2. Most peripheral myoepithelial cells were negative for P63 and SMMHC.

CONCLUSIONS: MCA is a rare primary breast cancer and strikingly similar to ovarian, pancreatic and gastrointestinal counterparts. The diagnosis cannot be made until the metastatic lesion is ruled out. On the other hand, the biologic behavior of MCA is reportedly favorable despite a high proliferation index and triple negative biomarker status. Therefore, the role of adjuvant chemotherapy or radiation is questionable.