CDKN1A and cancer: Finally, CKI gene expression analysis revealed elevated mRNA expression in malignant tumors for p16INK4a, p18INK4c, p19INK4d and p21CIP/WAF1 encoding genes, i.e. Cdkn2a, Cdkn2c, Cdkn2d and Cdkn1a, while p15INK4b and p27KIP1 encoding genes, i.e. Cdkn2b and Cdkn1b mRNA levels were unchanged between conditions (Figure 2C).