B Breast tumors do not all grow at the same rate or spread in the same way. And, it is not the size of a tumor that determines the aggressiveness of breast cancer but rather the tumor biology and microenvironment (the normal cells and molecules that surround cancer cells). Some breast cancers are small, found early, and yet are deadly. Some are fast growing. Some grow slowly, are found by mammograms and are treated, but would never have been life threatening.
Though we have known for some time that some breast cancers express excess estrogen receptors, we now know that there are several types of breast cancer based on the biology of the tumors. These subtypes respond to different treatments and have different prognoses. Though more will likely be identified in the future, breast tumors are currently classified using five immunohistochemical (IHC) tumor markers:
Based on expression of these markers, breast tumors are classified into the following subtypes:
Approximately 70% of “triple negative” breast cancers (TNBC) are basal-like; therefore, triple negative is often used as a surrogate for basal-like subtype. These different subtypes of breast cancer behave differently, are associated with different populations of women and different risk factors, and may have different causes.