Breast cancer is an abnormal growth of tissue in the breast that can sometimes be felt as a lump. The tumour develops when cells in the breast divide without control and produce extra tissue. It can be benign (non-cancerous) or malignant (cancerous). Cancerous cells can spread within the breast, to lymph nodes (glands) in the armpit and to other parts of your body.

According to the International Agency for Research on Cancer, there are approximately 2 million women around the world who were diagnosed with breast cancer in 2018, making it the most common cancer among women worldwide. Similarly, it is the most commonly diagnosed female cancer among Singaporean women. Almost 1 in 13 women in Singapore will be diagnosed with breast cancer in their lifetime. But what causes it and how can we prevent this type of disease?
Stages of breast cancer
Breast cancer is assessed in 5 stages:
- Stage 0: This stage is often referred to as ductal carcinoma in situ (DCIS). During stage 0, the cells are still limited to within a duct and have not yet started spreading to the surrounding tissues.
- Stage I: At this stage, the tumour is <2cm. However, it has not begun to affect the lymph nodes and other surrounding tissues..
- Stage II: The tumour is between 2 – 5cm, and may have started spreading to nearby lymph nodes..
- Stage III: The tumour has become >5cm and/or has spread to surrounding lymph nodes and surrounding tissues. It may have also invaded the skin or chest wall..
- Stage IV: The cancer has spread to distant body organs such as the brain, liver, and lungs..
Stage 0 and 1 breast has close to 100% relative survival rates at 5 years, while Stage 2 and 3 breast cancers have lower 5-year relative survival rates of 90% and 70% respectively. Stage 4 breast cancer, however, has a relative 5-year survival rate of 23%.
Types of breast cancer
There are 2 most common types of breast cancer among women – invasive ductal carcinoma (IDC), where cancer cells grow from within the ducts and invades the surrounding breast tissue, and invasive lobular carcinoma (ILC), which originates from the breast lobules and invades the surrounding tissue. These 2 types of breast cancer account for 70 – 80% and 10 – 15% of all breast cancers respectively.
There are other rarer forms of breast cancer like mucinous, papillary and tubular carcinomas. These usually have better prognoses than ductal and lobular cancers.
Paget’s disease of the nipple is a condition when breast cancer manifests as changes of the nipple, usually as a rash, and may be mistaken for eczema. An associated breast cancer is typically diagnosed on further imaging of the breast, although the cancer is rarely limited to the nipple.
Inflammatory breast cancer is an uncommon but aggressive form of breast cancer. The breast has a red and swollen appearance, sometimes without the presence of a breast lump. When what appears to be breast infection (mastitis) does not resolve with antibiotic treatment, a biopsy is required to exclude inflammatory breast cancer.