Chemotherapy is a combination of medicines that kill cancer cells by stopping their cellular division (mitosis) and “birthing” of new cancer cells. If cancer cells cannot give birth to new cancer cells, then the cancer itself will die. Chemotherapy is not very specific to cancer cells only, as chemotherapy also kills rapidly dividing healthy cells, which leads to many of the side effects of chemotherapy.
When we talk about how aggressive cancer is, we really want to know what is the chance the cancer has left the breast and landed somewhere else in the body. Are there small nests of cancer cells in the lungs, liver, or bones? If the chance is high enough, i.e. if the cancer is high grade, then chemotherapy may be recommended to kill these small nests of cells that we cannot see, before they divide and give birth to more and more cancer cells.
Since chemotherapy has some pretty nasty side effects, it would be helpful to identify those women who have low-grade cancers and do not need chemotherapy from those who have high-grade cancers and need chemotherapy. Women with Triple Negative Breast Cancers need chemotherapy. Women with Her2-positive breast cancers need chemotherapy. Women with Estrogen Receptor-positive (ER+) breast cancers may need chemotherapy if the cancer is bigger than 2cm or if the cancer has spread to the lymph nodes in the axilla (armpit).
The biology or behavior of the cancer is the information we need to address the need for chemotherapy. Those ER+ cancers with high-grade biology will be those that grow bigger and spread to the lymph nodes. But low-grade cancers can still grow large if given enough time and high-grade cancers can be quite small if caught early. So, is there a way to identify the biology of the cancer without measuring the size of the tumor or identifying whether it has spread to the lymph nodes?
Genetic profiling of tumors has been possible for over ten years now. And we now have two studies published in the New England Journal of Medicine, demonstrating that low-grade cancers, as defined by the test, do not need chemotherapy. OncotypeDx is the original test and if your cancer has a low recurrence score (<10), then all you need is an anti-estrogen pill and no chemotherapy. MammoPrint is another test and if your tumor has a low genomic score, then all you need is an anti-estrogen pill and no chemotherapy.
Do you need chemotherapy? If you have Triple Negative Breast Cancer or Her2+ Breast Cancer, then yes. If your cancer is ER+, greater than 2cm or with positive lymph nodes, you probably need chemotherapy. Women with cancers less than 1cm generally do not need chemotherapy. Women with cancers between 1-2 cm should have a genomic test performed on their breast cancer. Likewise, women with breast cancer tumors less than 1cm that may be high grade, should have a genetic profiling test and women with breast cancer cancers that are larger than 2cm or that have spread to the axillary lymph nodes but may be low grade, can consider a genetic profiling test in the hope of avoiding chemotherapy.
Ultimately, you and your medical oncologist need to decide if you need chemotherapy. The grade, size, lymph node status, receptor status and genomic testing can all provide useful information to help you and your medical oncologist decide on the right treatment for you.