CDKN1A and adult T-cell leukemia/lymphoma: Although expression of p21CIP1/WAF1 has been reported to be increased in HTLV-I-transformed cells in vitro [71], additional studies revealed that p21CIP1/WAF1 expression was frequently downregulated through promoter hypermethylation in acute ATLL cells, complete methylation was found in 25% of patients, and partial methylation was found in 70% of ATLL patients [72].