Revisiting Metaplastic Carcinoma of Breast: An Emphasis on the Clinico-pathological and Immunohistochemical Variables Analyzed at a Tertiary Cancer Centre in South India

BACKGROUND & OBJECTIVE: Metaplastic carcinoma is a diverse variant of invasive breast carcinomas (IBC) characterized by dedifferentiation of malignant cells towards squamous and/or mesenchymal elements. It accounts for 0.3-1.2% of all IBC. These tumors are typically triple-negative by hormonal profiling with a high proliferation index and a dismal prognosis. Lymph node metastasis is an unusual feature in metaplastic carcinoma. METHODS: The present study analyses 30 cases (26 cases of modified radical mastectomy and 4 cases of lumpectomy) of metaplastic carcinoma over 2018-2020 (3 years). Four oncopathologists reviewed routine histopathologic and immunohistochemical-stained slides. The clinical details were collected from the Medical Records Department of the Cancer Institute. RESULTS: A total of 20 (66.67%) cases were patients >50 years of age, 21(70%) out of which were diagnosed as invasive carcinoma, grade 3 according to the Nottingham histological score. Five (16.7%) cases presented with lymph node metastasis. While immunohistochemically 28 (93.3%) cases were triple-negativeCK5/6, P63, EGFR, and Ki-67 (more than 40%) positivity was noted in 25 (83.3%) , 26 (86,7%) , 20 (66.7%), and 25 (83.3%) cases, respectively. CONCLUSION: Metaplastic carcinoma is characteristically triple-negative breast malignancies (TNBC) exhibiting a high Ki-67 index and a lower rate of lymph node metastasis. CK5/6, p63, and EGFR are pertinent immunohistochemical markers that may aid in diagnosis. However, those markers are non-specific for the disease and morphologic features are always the key to diagnosis of the process.