Understanding Breast Cancer: Types, Risk Factors, and Advances in Detection

Breast cancer is the most commonly diagnosed cancer among women worldwide and contributed to an estimated 694,000 deaths in 2024. Diagnosis rates are rising in some populations, including among women under 50. Although breast cancer is much more common in women, men can also develop it because they have breast tissue. Breast cancer is a disease in which abnormal cells grow uncontrollably in the breast and eventually form a tumour, or lump-like mass. It commonly begins in the milk ducts or milk-producing lobules. At an early, non-invasive stage, it has not spread into surrounding breast tissue. However, as cancer cells invade nearby breast tissue, they can form tumours that may cause lumps or thickening. Invasive cancers can spread to nearby lymph nodes or other organs through a process called metastasis, which can make them life-threatening.

Breast cancer can be divided into two broad categories: invasive and non-invasive. When invasive breast cancer is diagnosed, it means that cancer cells have spread beyond their original location into surrounding breast tissue. They can also spread to lymph nodes in the underarm area. Invasive ductal carcinoma is the most commonly diagnosed type of breast cancer, accounting for approximately 70% to 80% of cases, while invasive lobular carcinoma accounts for around 10% to 15%. Non-invasive breast cancer refers to abnormal cells that remain contained within the milk ducts or lobules and have not invaded surrounding breast tissue. Ductal carcinoma in situ (DCIS) is often referred to as stage 0 or non-invasive breast cancer. Lobular carcinoma in situ (LCIS), however, is not breast cancer itself. Instead, it is a condition associated with an increased risk of developing breast cancer in the future. If left untreated, DCIS can sometimes develop into invasive breast cancer. Other uncommon forms of breast cancer include inflammatory breast cancer and Paget’s disease of the breast. Triple-negative and HER2-positive breast cancers are also important subtypes, classified according to the characteristics of the cancer cells. Breast cancer is staged from 0 to IV, with stage IV being the most advanced and indicating that the cancer has spread to distant parts of the body.

The key risk factors for breast cancer can be divided into modifiable and non-modifiable factors. Modifiable factors are those that can potentially be changed, while non-modifiable factors cannot. Modifiable risk factors include body weight and obesity, physical activity, hormone replacement therapy, and alcohol consumption. Non-modifiable factors include age, genetics, biological sex, and family history. Because every cancer develops from a unique combination of cellular changes and mutations, breast cancer varies from person to person. Different types of breast cancer may therefore require different treatment approaches. Treatments can include chemotherapy, immunotherapy, radiotherapy, targeted therapy, and hormone-blocking therapy.

Current research into breast cancer focuses partly on improving early detection and identifying people at higher risk of developing the disease. Mammography is an established screening method used to detect breast cancer. Artificial intelligence (AI) tools are also being developed to analyse mammography scans, assist radiologists, and estimate a patient's risk of developing breast cancer in the future, including over a five-year period. These tools may help identify individuals who could benefit from closer monitoring and support clinical decision-making. However, AI-based risk predictions are not guarantees that an individual will or will not develop cancer. Overall, research is helping improve the detection and treatment of breast cancer. In the United States, approximately 1 in 8 women and 1 in 800 men will develop breast cancer during their lifetime. These estimates vary between populations and countries. This is why it is important to raise awareness and reduce the stigma surrounding breast cancer as a disease that affects only women.