Molecular Subtypes of Breast Cancer According to Immunohistochemical Expression of Hormone Receptors in A Region of North West India: A Comparative Study with Other Regions in India and Around the Globe

Background: Breast cancers have been subclassified on the basis of molecular expression. This study evaluates the receptor expression in breast carcinoma by immunohistochemistry and classifies them into various subtypes. A comparison with other regions was also made. Methods: This prospective study included all the patients of breast carcinoma who had undergone the surgical treatment of mastectomy at SMSMC from January 2014 to June 2017. Immunohistochemical expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER-2) was studied and subtypes were determined. Comparison of the receptor expression and patterns was done in different age groups and with other regions. Results: ‘A total of 496 cases were included in this study. The mean age at diagnosis was 48.2 years. Most of the patients (60.3%) were less than 50 years old whereas 39.7% were above 50 years. By Bloom Richardson scoring 28.7%, 56.8% and 14.5% tumours were classified as Grade I, Grade II and Grade III respectively. ER, PR and HER2neu receptor positivity was seen in 57.5%, 44.1% and 26.6% respectively. The most common molecular subtype was luminal A (41.7%) followed by triple negative subtype (30.8%). Luminal B and HER2neu overexpressing types were 15% and 12.5% respectively. Conclusion: Immunohistochemical markers act as surrogate markers for molecular classification of breast cancers. Hormone receptor expression at our institute was comparable with other studies from India. Luminal A is the most common occurring subtype of breast cancer presenting at our institute.