In MCF-7 human breast cancer cells, chronic competitive inhibition of SNAT2 progressively reduced cell proliferation and induced a significant decline in intracellular concentrations of not only SNAT2 AA substrates (e.g., serine, glutamine, alanine, threonine) but of branched chain AAs (leucine, isoleucine and valine). This evidence concerns the gene SLC38A2 and breast cancer.