St. Gallen's molecular subtypes in primary breast carcinoma in Indian population

Aim: Immunohistochemical (IHC) markers have been used as surrogates for DNA-microarray in subtyping breast cancer, which lead to new biological insights and eventually to better-targeted therapies. Our study aimed at studying the distribution of the St. Gallen's molecular subtypes in our population and to evaluate their association with traditional prognostic features. Materials and Methods: Seventy-five cases of primary breast cancer undergoing radical or modified radical mastectomy were classified into five subtypes based on their IHC profile using estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 (Her2)/neu, and Ki-67 as per St. Gallen's guidelines. IHC subtypes were correlated with various clinicopathologic prognostic parameters including age, tumor size, tumor type, axillary lymph node status, and histologic tumor grade. Results: The proportion of each subtype in our population was: luminal A 28%, luminal B Her2− 18.7%, luminal B Her2+ 9.3%, Her2/neu+ 17.3%, basal cell-like (BCL) 26.7%. The majority of luminal A cases were well differentiated (Grade I) whereas luminal B Her2− was mostly moderately differentiated (Grade II) and luminal B Her2+ constituted mainly well differentiated and moderately differentiated tumors. Both subtypes of luminal B showed lymph node metastasis in majority of the cases. Her2/neu+ and BCL subtype were high-grade tumors comprising mainly of moderately differentiated and poorly differentiated tumors. The majority of luminal A cases were negative for Ki-67 whereas all the luminal B Her2− tumors expressed Ki-67, 50% being highly positive. BCL subtypes revealed highest proliferation index with 80% of the cases being high positive Ki-67. A statistically significant difference of modified Bloom–Richardson grade and Ki-67 distribution (χ² = 42.974; P< 0.001) between various IHC subtypes was observed.