Molecular types of breast cancer

Not all breast cancer tumours are the same, in fact, there are quite a few sub-types of breast cancer and they are broadly broken into four groups based on their molecular signature, or lack thereof.

Tumour cells have certain hormones and protein receptors which are naturally found in women’s bodies, and knowing what sub-type of breast cancer they are dealing with allows doctors to determine the specific needs of each individual, and determine a treatment plan according to the molecular make-up of their tumour. For example, about 70 per cent of breast cancers test positive for hormone receptors which means treatments can target those receptors and effectively reduce or kill the cancer cells.

As a result of breakthrough discoveries, we have seen the treatments for breast cancer evolve of from a one-size-fits-all approach to a highly sophisticated precision medicine. However, at this stage, there are still types of breast cancer for which receptors and proteins have not yet been identified and so effective treatments are yet to be developed, and research continues to play an essential role in closing this gap in our knowledge of the disease.

Understanding the complexity and differences between tumours, what they respond to and what they don’t, is why the National Breast Cancer Foundation doesn’t talk about a ‘cure’. We know that a single big breakthrough or new treatment won’t work for all breast cancers. Each tumour is different, and each patient is different, so treatment for each will be different too. We know a lot about breast cancer, but there is still more research to be done to fully understand the complexity of this disease.

Estrogen-receptor positive breast cancer

Breast cancers with receptors for the hormone estrogen are called estrogen-receptor positive or ER-positive breast cancer. They respond well to treatment with hormonal therapies such as tamoxifen. Estrogen-receptor negative or ER-negative breast cancers don’t have hormone receptors.

Progesterone-receptor positive breast cancer

Breast cancers with receptors for the hormone progesterone are called progesterone-receptor positive or PR-positive breast cancer. They respond well to treatment with hormonal therapies.

HER2-positive breast cancer

HER2 (human epidermal growth factor) is a protein that can affect the growth of some cancer cells. It is found on the surface of normal breast cells.  Some breast cancer cells have a very high number of HER2 receptors. The extra HER2 receptors stimulate the cancer cells to divide and grow. This is called HER2 positive breast cancer. HER2 positive breast cancers tend to grow more quickly than HER2 negative breast cancers. HER2-positive breast cancers can be targeted with Herceptin treatment.

Triple negative breast cancer

Triple-negative breast cancer is any breast cancer that tests negative for all three of the above hormone or protein receptors. Triple negative breast cancers are difficult to treat because they do not have these receptors and therefore a targeted therapy has not yet been developed for this sub-type of breast cancer. These tumours are typically more aggressive and have a higher presence among younger women diagnosed with breast cancer younger women.