Surrogate molecular subtyping of breast carcinomas– A study on recent modifications and their clinicopathological significance

Abstract

Context: Breast carcinoma is a heterogenous disease with varied clinicopathological features andresponse to therapy. Molecular classification through gene studies helps in planning therapy but haseconomic constraints. Hence immunohistochemical subtyping of breast carcinomas has been used asa surrogate method. Criteria for this subtyping has undergone many modifications since it wasoriginally proposed. Objectives: To immunohistochemically subtype breast carcinomas based onSt.Gallen 2017 guidelines and analyse the differences in clinicopathological parameters like age,tumour size, histopathological grade and lymph node staging between the various subtypes.Materials and methods: The study was done retrospectively at a tertiary care health centre inSouth India on breast carcinoma patients from January 2017 to June 2020. Immunohistochemistrywas done with antibodies to the Estrogen receptor, Progesterone receptor, Human epidermal growthfactor receptor-2 (HER-2) and Ki-67. Immunohistochemical Subtypes were correlated withClinicopathological features. Results: The study had 107 cases. Hormone receptor (HR) positiveHER-2 negative was the most common subtype (55 cases, 51.4%). This subtype frequentlypresented without nodal metastasis (58.2%) and in >50 years of age (56.4%). Triple-negativesubtype frequently presented with grade III (69.2%), highest nodal metastasis stage (38.5%) andin < 50 years of age (69.2%). Conclusion: St.Gallen 2017 guidelines for immunohistochemicalsubtyping classified breast carcinomas into groups that differed significantly in theirclinicopathological features. Further studies on differences in treatment response and survival ratedifferences between these different subtypes are needed.