Molecular types of breast cancer
Not all breast cancer tumours are the same, in fact, there are quite a few subtypes 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 subtype 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 (human epidermal growth factor) is a protein that is found on the surface of normal breast cells and can affect the growth of some cancer cells. Some breast cancer cells have a very high number of HER2 receptors – theses stimulate the cancer cells to divide and grow into what is called HER2 positive breast cancer. HER2 positive breast cancers tend to grow more quickly than HER2 negative breast cancers and some other breast cancer types. HER2-positive breast cancers can be targeted with Herceptin treatment.
One of the key breakthroughs in saving lives over the past 20 years was the discovery of the HER2 positive subtype of breast cancer. Once identified, researchers were able to develop a targeted therapy called Herceptin which works by attaching itself to the HER2 receptors on the surface of breast cancer cells and blocking them from receiving growth signals.
This means that women with HER2 positive breast cancer no longer rely on standard treatments in the hope that they will work – now there is an effective therapy designed specifically to prevent their type of breast cancer from growing or spreading. Researchers are also looking at other diseases that could benefit from Herceptin, such as lung cancer and pancreatic cancer, so its benefits can be felt as far and wide as possible.
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.