Different types of breast cancer can behave and respond differently to various treatments. To understand why, researchers study which genes are active in tumor cells. These patterns help them identify groups of tumors with shared characteristics. Basal-like breast cancer is one of those groups.
In basal-like breast cancer, the tumor cells use a combination that resembles that of normal basal cells, which form the outer layer of the breast’s milk ducts. This similarity in gene activity gives the subtype its name. By grouping tumors this way, researchers can study why they behave differently and look for new ways to treat them.
How is basal-like breast cancer different from other types?
Basal-like breast cancer often has two features:
- Triple-negative status: The tumor cells lack estrogen receptors (ER) and progesterone receptors (PR) and do not overexpress the HER2 protein. Tumors with these findings are called triple-negative breast cancers (TNBCs).
- High grade: The cells look very abnormal under a microscope and tend to grow and divide quickly.
These attributes come together so often that some people use the terms basal-like and TNBC interchangeably. However, we must keep in mind that these terms describe different features of the cancer and do not mean the same thing. Basal-like describes a pattern of gene activity, while triple-negative describes receptor status. Most basal-like tumors are triple-negative, but not all are, and not all triple-negative tumors are basal-like.
What causes basal-like breast cancer?
Scientists have some explanations for why someone develops cancer. Breast cancer, specifically, is often caused by genetic mutations that disrupt the control of cell growth and division or the repair of damaged DNA. When that happens, cells can start to grow uncontrollably.
Most of these genetic mutations are acquired during a person’s lifetime and, less commonly, someone can be born with a mutation that increases their risk of developing breast cancer. The best-known genes related to these inherited mutations are BRCA1 and BRCA2.
That said, researchers still don’t fully understand what causes basal-like breast cancer. What science does know is that some subtypes are more commonly seen in people with certain risk factors. Basal-like breast cancer is more common in younger, premenopausal women, Black women and those with an inherited harmful BRCA1 gene mutation.
How is basal-like breast cancer diagnosed?
Doctors diagnose breast cancer through a biopsy, which involves removing a small sample of breast tissue and examining it for cancer cells. The tumor is then tested for estrogen receptors, progesterone receptors and HER2 to determine whether it is triple-negative. However, these results alone do not confirm that it is basal-like.
Identifying this molecular subtype requires examining the pattern of gene activity in the tumor. This test is usually performed in research settings, when scientists need to investigate the cancer’s behavior and response to treatment. Most patients do not need it to begin treatment.
How is basal-like breast cancer treated?
As with all types of breast cancer, treatment depends on the cancer’s stage, receptor status and other test results. All treatment plans must be personalized to target the specific type of cancer cells one might have.
The options include surgery, chemotherapy, radiation or a combination of treatments. Some patients also receive targeted therapy, depending on the tumor’s features and whether they have certain inherited mutations, or immunotherapy, which helps the immune system fight cancer.