20th June 2023

Risk Factors

Genetic, hormonal, and environmental factors play a role in the pathogenesis of breast cancer. ~5-10% of breast cancers are due to mutation in BRCA1, BRCA2, AT or TP53 genes. BRCA1 and BRCA2 genes are located in chromosomes 17q and 13q respectively, and both genes function as tumour suppressor genes. Human epidermal growth factor receptor 2 (HER2) is a membrane tyrosine kinase and proto-oncogene that is overexpressed in about 25-30% of breast cancers. It is located in the long arm of chromosome 17 (17q12). Hormonal factors, particularly oestrogen exposure, are also one of the significant risk factors for breast cancer. Reported risk factors include nulliparity, first pregnancy >30 years old, early menarche, late menopause, long term use of HRT in postmenopausal women. Short-term use of HRT may not be associated with a high risk of breast cancer. Alcohol intake, physical inactivity and obesity are also related to an increased risk of breast cancer. Prior radiotherapy to the breast or chest wall also increases the risk.