Descriptive study of the histopathological subtypes and programmed death-ligand 1 in metaplastic breast carcinoma.

Metaplastic Breast Carcinoma (MBC) is a rare heterogeneous group of tumors, the incidence of which is less than 1% of breast tumors. These are a unique set of tumors with varying subtypes, poor prognosis, and an increased chance of distant metastasis. We aimed to study the clinical, histomorphological, and immunohistochemical (IHC) features of Metaplastic Breast Carcinoma (MBC). This was a descriptive study of cases diagnosed as MBC at a tertiary care center in Southern India from January 2015 to December 2019. A total of 20 cases were diagnosed whose clinical, histomorphological, and IHC features were studied. PD-L1and CD8 IHC were performed and analyzed in 12 cases. The median age of presentation was 50 years. Seventy percent (14/20) patients were postmenopausal women. On excision, 75% (15/20) showed mixed typed MBC, the remainder showing epithelial type MBC. Metastasis to axillary lymph node was seen only in 20% (4/20) of the cases. Thirty percent (6/20) of the cases belonged to stage 3 disease and 5% (1/20) of the cases belonged to stage 4 disease with liver metastasis. Estrogen receptor (ER), Progesterone receptor (PR) were negative in all the cases, Her2neu was positive in three cases. Ki67 labeling index was greater than 14% in all the cases. PD-L1was positive in 41.5% of the cases and intratumoral CD8 positive lymphocytes were increased in 83.3% of the cases. MBCs are tumors occurring in elderly postmenopausal women, presenting with large tumor size, have lesser chances of lymph node metastasis, and a higher chance of recurrence and hematogenous spread. They are negative for ER, PR, Her-2 neu, with a high Ki67 index and a strong PDL-1 expression.