Breast cancer (BC) is the most common type of cancer in women (24.5%). BC can arise in different parts of the breast. Breast is divided in to three parts: lobules, ducts, and connective tissue. Lobules are gland which produces milk and ducts which carry milk to the nipples. The connective tissue surrounding everything holds together. Most of the breast cancers begin either in ducts or lobules. In women, BC is the leading cause of cancer death, followed by colorectal and lung cancer. Incidence rates of breast cancer are rising fast in transitioning countries such as South America, Africa as well as in high-income Asian countries (Japan and the Republic of Korea), where rates are historically low. In India, BC is the first most common cancer among women aged 15-45 years and accounts for 25% of all cancers in women.
BC develops as a new mass or lump. It may be painless, hard-mass with irregular edges but the cancer tissue can also be soft, round, tender and be painful. In general, BC is divided into Invasive Ductal Carcinoma (IDC) and ductal carcinoma in situ (DCIS). IDC is also known as infiltrating ductal carcinoma that develops in a milk duct and invades the fibrous or fatty tissue of the breast outside of the duct. DCIS is a non-invasive condition in which abnormal cells are found in the lining of a breast duct.

BC is heterogeneous disease that involves many risk factors such as age, family history, sex, estrogen, gene mutations, epigenetic mechanisms, unhealthy lifestyle etc. Majority of the cancers are caused by inherited genetic factors, including breast cancer. The genes are associated with germline and somatic mutations in breast cells that are inherited and acquired during a woman's lifetime. Based on genetic mutations breast cancer risks are classified into moderate risk, moderate to high risk and uncertain risk. The bar chart shown below explains the majorly associated genes with breast cancer with their percentage and their lifetime risk scores. The mutations in genes like BRCA1, BRCA2, TP53, PALB2, STK11 and CH3K2 initiate the development of BC. There are other initiators like hormones, chemicals, radiation etc which are either causative or supportive of genetic mutations in the development of breast cancer.