As CHK2 activation has been found to be responsible for the induction of p21 expression in p53-deficient SK-BR-3 breast cancer cells and HaCaT immortalized keratinocytes [24], we were interested in determining whether CHK2 is activated in cyproheptadine-treated Huh-7 cells in which p21 expression is up-regulated. The gene discussed is CHEK2; the disease is breast carcinoma.