In short, antagonists of tryptophan hydroxylase 1 (TPH1), monoamine oxidase A (MAO-A), SERT and each of 5 of the 17 5-HTRs inhibited tumorsphere formation by each of six human breast tumor cell lines independent of the breast cancer subtype that they model [18, 19]. The gene discussed is TPH1; the disease is breast carcinoma.