Histopathological Variants and Molecular Subtypes of Carcinoma Breast in a Tertiary Care Centre, Kerala, India: A Cross-sectional Study

Abstract

Introduction: Breast cancer is the second leading cause of cancer deaths in women after lung cancer. Breast cancer survival varies by racial and ethnic factors, stage at diagnosis, tumour grade, molecular subtypes and the treatment received. Molecular subtyping provides prognostic and predictive information about the risk of recurrence and is an essential tool in formulating guidelines in therapy. Aim: To identify the histopathological variants of Carcinoma (Ca) breast in women and to determine the various molecular subtypes by Immunohistochemistry (IHC). Materials and Methods: A cross-sectional study from January 2019 to December 2020 was done on 100 cases of invasive carcinoma breast at the Department of Pathology in a tertiary care center of Government Medical College, Ernakulam, Kerala. IHC was done on paraffin processed tissue sections of tumour using anti-Oestrogen Receptor (ER), anti-Progesterone Receptor (PR), anti-Human Epidermal growth factor Receptor 2 (HER2/ neu) and Ki-67 antibodies. Molecular subtypes of Luminal-A, Luminal-B, HER2 enriched and triple negative (basal-like) were determined. The association between molecular subtypes and tumour grade, size, stage was analysed using IBM Statistical Package for the Social Sciences (SPSS) version 21.0 software. Chi-square test used for categorical variables, p-value <0.05 assumed to be significant. Results: Total 100 female cases of invasive carcinoma breast with mean age 49.3±12.2 years were included. Histologic subtypes of carcinoma were: Invasive Ductal Carcinoma (IDC) of No Special Type (NST) (89%), Invasive Lobular Carcinoma (ILC) (1%), Invasive ductal with Lobular carcinoma (IDC-L) (1%), metaplastic (2%), papillary (4%), IDC with medullary like features (3%). Tumour size was pT1 in 27%, pT2 in 38%, pT3 in 33%, pT4 in 2%. Tumour grades were: grade-I (28%), grade-II (29%) and grade-III (43%). Lymph node metastasis was seen in 52% cases. Positive expression of Oestrogen (ER) in 46%, Progesterone (PR) in 38%, HER2/neu in 23% and low Ki-67 labeling index (<14%) in 32% cases were observed. The molecular subtypes were Luminal-A (32%), Luminal-B (14%), HER2 enriched (16%) and triple negative (38%) in the present study. Conclusion: The most common molecular subtype was triple negative. Luminal-A subtype was associated with lower histologic grade and non luminal subtypes were associated with higher histologic grades. To determine molecular subtypes, IHC is useful as a surrogate for molecular testing.