In patients with breast cancer, abnormal cells develop in the breast and form tumours which invade the surrounding breast tissue.

Breast cancer can occur in both males and females, though male breast cancer accounts for less than 1% of all breast cancer cases.

How does breast cancer develop?

Breast cancer develops when cells in the breast grow in an abnormal way and form tumours.

The female breast is comprised of milk-producing glands called lobules, ducts which carry milk from the lobules to the nipples, and fatty and connective tissue.

Most cases of breast cancer begin in the cells that line the ducts, while others can begin in the cells that line the lobules.

When cancer is confined to either the ducts or lobules, it is classed as non-invasive. If it spreads, it is referred to as invasive breast cancer.

How does breast cancer spread?

Breast cancer spreads when tumour cells break away from the mass and travel via the bloodstream or lymphatic system to other tissues in the body, where they start multiplying again. This process is called metastasis.

The location where cancer develops is known as the primary site. Cancer that forms as a result of spreading from the breast is referred to as metastatic, secondary or advanced breast cancer.

What causes breast cancer?

While the specific causes of breast cancer are not yet known, scientists have identified a series of risk factors that may increase the chance of cancerous cells forming in the breast.

Inherited gene mutations and acquired gene mutations are thought to be two of these risk factors. Inherited gene mutations, such as the BRCA genes (BRCA1 and BRCA2), are genes that suppress tumour growth. Many women with these mutated genes have a higher probability to develop cancer, though the genes don’t actually cause the cancer.

Acquired gene mutations may occur in the breast as a result of factors like chemical or radiation exposure.

Other risk factors for breast cancer can include being female, increasing in age, a family history of breast cancer, a personal history of breast cancer, hormonal factors and lifestyle factors.

What different types of breast cancer exist?

Breast cancer can occur in the ducts of the breast (ductal carcinoma in situ or DCIS) or the lobes of the breast (lobular carcinoma in situ or LCIS).

When breast cancer is detected early, it is usually confined to the breast and may not have spread. It’s not always possible to detect whether cancer cells have spread.

Advanced breast cancer is invasive (aggressive) breast cancer that may have spread either locally or to other parts of the body. In rare cases, advanced breast cancer can affect the lymphatic vessels in the skin of the breast.

Infrequently, breast cancer can affect the nipple and areola, though this is often a secondary cancer associated with invasive breast cancer elsewhere in the breast.

Breast cancer treatment and prevention

Breast cancer is the most common cancer among women, with nearly 1.7 million new cases diagnosed in 2012.

Screening, early detection, increased awareness and constantly improving treatments are helping to gradually improve breast cancer survival rates.

Treatment depends on the stage and severity of breast cancer. Other factors, such as signs and patient health, may also impact the treatment approach.

Common forms of breast cancer treatment include surgery to remove part or all of the affected breast, surgery to remove one or more lymph nodes from the armpit, radiation therapy and chemotherapy.

An emerging body of research is indicating that knowing a tumour’s genomic profile could be more important for successful treatment than knowing its location or size. As each tumour’s genomic profile is unique, this approach is often referred to as personalised or precision medicine.

Raising awareness of the well-established breast cancer risk factors, encouraging patients to learn their family history, and referring at-risk patients for regular screening checks risk are all important preventative measures.