Prevalence of molecular subtypes of breast cancer: Experience in a tertiary care cancer centre in Sri Lanka

Breast cancer is the commonest cancer among females. Patient outcome and treatment options are largely influenced by its molecular subtypes. This study aims to evaluate molecular subtypes of breast cancers among patients treated at a tertiary cancer centre in Sri Lanka. Clinical and demographic data were collected retrospectively from electronic medical records available at the cancer institute, Maharagama, Sri Lanka. Histology reports of 200 patients who had undergone mastectomy or wide local excision during an 18-month period starting from January 2018 were analyzed. Patients' age, histological subtype of cancer, receptor status of estrogen receptor (ER) progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), Ki-67 index, and tumour grading were considered. The age range of the patients was 29 to 84 years (mean=57.7, SD=11.76). The 50-59 and 60-69 age groups represented the most patients (28% each). Females represented 99% (n=199) of the total while three patients had bilateral breast cancer. Histologically, invasive carcinoma of no special type (NST) was the commonest cancer type (n=178, 89%), with the majority being grade 2 cancers (52.5%) according to the Nottingham cancer grading (grade 1=15.1% and grade 3=32%). Luminal A was the most common (64%) molecular subtype, followed by basal-like (21%), HER2-enriched (11.5%), and luminal B (4.5%). Data on the Ki-67 index was available for only 98 patients, and 8.1% (8) of them had a Ki-67 index less than 10, while 22.5% (n=22) between 10 and 20. All others (69%) had a higher Ki-67 index (>20). There is a significant association between the molecular subtype of breast cancer and Nottingham grading (p Majority of Sri Lankan women with breast cancers present in the 5th and 6th decades of their lives. Luminal A molecular subtype was the predominant, followed by basal-like, HER2- enriched, and luminal B. Aggressive HER2- enriched and basal subtypes are more common in younger age groups. We recommend breast cancer subtyping before surgery so that more people will benefit from neoadjuvant chemotherapy.