What is breast cancer?

Breast cancer is an abnormal growth of cells within the breast. Most commonly it arises from the cells lining the milk ducts (ductal cancer) or milk-producing lobules (lobular cancer). However, it can arise from any cells within the breast.

If the cancer cells stay within the duct/lobular system it is called in situ cancer. If the cancer cells invade through the duct/lobular system into the surrounding breast tissue, it is called invasive breast cancer.

 

What are breast cancer subtypes?

A more contemporary and useful way of dividing breast cancer into subtypes is using the receptor status on the pathologic analysis. Breast cancer cells may or may not express estrogen and/or progesterone (so-called hormone-positive or negative). The other receptor is called Her2 which if overexpressed can be responsible for the rapid growth of cancer cells.

Based on these three receptors, breast cancer can be divided into the following 4 subtypes:

• Hormone receptor + / Her2 –
• Hormone receptor + / Her2 +
• Hormone receptor - / Her2 +
• Triple-negative (Estrogen, progesterone, and Her2 negative)

The importance of this classification is its implication in the treatment of breast cancer. For example, a patient with hormone-positive breast cancer will benefit from anti-hormone therapy. Similarly, a patient with Her2 + breast cancer will benefit from specific anti-Her2 medications which are administered along with chemotherapy. On the other hand, patients with triple-negative breast cancer most often will need chemotherapy as none of the other systemic therapies is going to be effective. 

 

What causes breast cancer?

The most important risk factors for breast cancer are female sex and age. Women are 100 times more likely to get breast cancer than men. The risk increases with advancing age: 75 per cent of breast cancers occur after the age of 50.

Genetics play an important role in only 5-10 per cent of breast cancers. In other words, 90 per cent of breast cancers are so-called sporadic (by chance). Based on the number of affected first and second-degree relatives with breast or ovarian cancer, women are divided into three categories:

• Average risk: 1 in 11 to 1 in 8 chance of breast cancer by the age of 75.
• Moderate risk: 1 in 8 to 1 in 4 chance of breast cancer by age of 75.
• High risk: More than 1 in 4 chance of breast cancer by age of 75.

If you have multiple family members with a history of breast cancer especially at a young age, or any relative with a history of ovarian cancer, or breast cancer in a male relative it is important to see a breast specialist to go through your family history and determine your risk.

 

Can I reduce my risk of breast cancer?

There are some ‘so called’ modifiable breast cancer risks factors such as obesity, alcohol use, high fat diet, and sedentary lifestyle. Although each one in isolation is considered a minor risk factor, the presence of multiple of these risk factors together can add up to a substantially increased risk of breast cancer.

The prolonged combined hormone replacement therapy in postmenopausal women has also been shown to increase the risk of future hormone-positive breast cancer, and therefore risk and benefit should be considered on an individual basis.

In women with a high risk of familial breast cancer, risk-reducing interventions may be discussed. The most effective risk-reducing strategy is bilateral mastectomy which reduces future risk of breast cancer by 90-95 per cent. The other option is taking tamoxifen which reduces the risk by about 50 per cent.