MCF7 (mildly malignant, ER-positive, wild-type p53; functional deletion in the caspase 3 (CASP3) gene) and MDA-MB-231 (malignant, ER-negative, mutant p53) breast cancer cell lines were chosen as an in vitro experimental model of human solid tumors. The gene discussed is CASP3; the disease is breast carcinoma.