This correlation has only been observed in specific patient populations but in light of our study demonstrating that the binding partner for tacrolimus, FKBP12, is expressed in the vasculature of human breast tumors, and that tacrolimus inhibits the growth rate of MMTV-neu transgenic breast carcinomas in mice, there is good rationale for prospectively investigating the clinical utility of tacrolimus in breast cancer treatment. The gene discussed is FKBP1A; the disease is breast carcinoma.