The effect of nonphosphorylated peptide 41 on the proliferation of SK-BR-3 breast cancer cells, which express high levels of the Grb7 protein [32], was evaluated using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4- sulfophenyl)-2H-tetrazolium, inner salt) cell proliferation assay. This evidence concerns the gene GRB7 and breast carcinoma.