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Abstract
Cell - free DNA circulating in blood is a candidate biomarker for malignant tumors. Unlike uniformly truncated DNA released from apoptotic non diseased cells, DNA released from dead cancer cells varies in size. To measure the ratio of longer to shorter DNA fragments (DNA integrity) in serum to study it as a potential biomarker for patients with colorectal cancer (CRC). Sera from 50 patients with CRC,10 patients with benign colonic lesions and 20 healthy volunteers were assessed by quantitative real-time PCR of ALU repeats (ALU-qPCR) with 2 sets of primers (115 and 247 bp) amplifying different lengths of DNA. DNA integrity was determined as ratio of qPCR results of ALU 247 - bp over ALU 115-bp. Serum DNA integrity was increased in cases of CRC at different stages indicating highly significant difference from control and premalignant groups (p < 0.001). ROC curves for differentiating CRC from control and from premalignant lesions had areas under the curves of 0.9 and 0.85 respectively