CDKN1B and breast cancer: This analysis included 9 candidate genes in 3 signaling pathways: (1) members of the CIP/KIP family of cyclin-dependent kinase inhibitors (CDKIs), p21CIP1/WAF1, p27KIP1, and p57KIP2 (2) members of the INK family of CDKIs, p15INK4B, and p16INK4A (3) members of the TGF-β family, TGFβI, TGFβII and the signaling receptors, TβRI, and TβRII. As illustrated in Figure 3A, we observed that in 10/12 breast cancer cell lines, p21CIP1/WAF1 levels were 2 to138 fold lower than steady state levels in normal breast epithelium.