ESR1 and triple-negative breast carcinoma: On the other hand, considering that triple-negative breast cancer (TNBC) is characterized by the lack of progesterone receptor (PR), estrogen receptor (ER), and HER2 overexpression, in this sense, Walsh et al. used an immunohistochemistry assay to measure the levels of mTOR and phospoho (p)-mTOR in 99 non-TNBCs and 89 TNBCs.