Previously, we have shown that Id1/3-PA7 regulates the expression of CDKN1A and CDKN1B in a dose-dependent manner in breast cancer cells MCF-7 and MDA-MB-231, which contain the homozygous deletions of the gene CDKN2A (Kamb et al, 1994). The gene discussed is CDKN1A; the disease is breast carcinoma.