ESR1 and cancer: Triple negative breast cancer (TNBC) is a breast cancer subtype characterized by the lack of expression of estrogen receptor (ER), progesterone receptor (PR) as well as HER-2 neu amplification (grade 3+ on immunohistochemistry (IHC) or fluorescent in-situ hybridization (FISH)-positive) on the cancer cells and constitutes about 15% of all breast cancers[1].