CDKN1A and colon carcinoma: Furthermore, it has been reported that an inhibition of apoptosis by ionizing radiation in p21Cip1/Waf1-/- colon carcinoma cells, in which no p21Cip1/Waf1-Caspase-3 direct association was observed, was due to a blockade of Caspase-9 and ultimately also Caspase-3 activation [23].