CCND1 and cancer: Cells with the mutant allele accumulate mutations as a result of defective mismatch repair and bypass the G1-S checkpoint of the cell cycle more easily than in cells not carrying the polymorphism.[30] Variant polymorphisms can result in abnormal protein levels and lead to cancer.[20] The CCND1 over expression has been reported to occur in 72% of colorectal tumors.[62] However, results of case-control studies about this genetic polymorphism were inconsistent.