RB1 and carcinoma: To identify the G1 kinase in colorectal carcinoma, we have shown that knockdown of CDK6 but not CDK4 markedly reduces RB phosphorylation and inhibits the growth of colorectal carcinoma cells, suggesting for the first time that CDK6-RB axis is crucial in the growth of the carcinoma and targeting of the CDK6-RB axis may provide a novel therapeutic strategy in the treatment of colorectal carcinoma.