In the recent times after genetic study of breast tissue a lot of information pouring in as regards its behavior. That has some bearing on the modalities of treatment. Though there are several genetic markers of this disease, extensively studied are; estrogen receptor (ER), progesterone receptor (PR) and ERBB2 or HER2 (Epidermal growth factor). Now researchers have been able to demonstrate that the cancer expressing particular type of genetic marker responds to a particular treatment e.g. ER positive cancer responds to tamoxifen, a estrogen receptor blocker.
So, in this way, it also has been seen that the breast caner negative for ER, PR and ERBB2/HER2 are aggressive and tagged with bad prognosis in comparison to cancers positive for these markers. And that is why a new classification is being advanced basing on the genetic behavior.
If these three genetic markers are absent in a breast caner, it is termed as triple negative breast cancer.