Moreover, since there is a possibility that NGF selectively influences the proliferation of breast cancer cells but not normal breast epithelial cells, NGF might be an optimal therapeutic target for particular cancer types [43]; the effect of NGF on cancer cells differs according to the expression status of TrkA and/or p75NTR and varies with the use of chemotherapeutic agents [44]. This evidence concerns the gene NTRK1 and breast carcinoma.