Circulating Cell Free DNA Integrity Index as a Biomarker for Response to Chemotherapy in Patients with Metastatic Colorectal Carcinoma

OBJECTIVE: Assessing plasma Cell Free DNA (cfDNA) integrity index as a biomarker for response prediction and early response evaluation in mCRC patients receiving chemotherapy, in comparison to Carcinoembryonic antigen (CEA) and Carbohydrate antigen 19-9 (CA19-9), to be used as an additional tool to computed tomography (CT). METHODS: CEA, CA19-9, cfDNA concentration and cfDNA integrity index (ALU 247/115) measurements were conducted on 86 subjects divided into 43 healthy volunteers and 43 mCRC patients, before starting chemotherapy and then after 6-12 weeks of therapy initiation (3-4 cycles FOLFOX) at first response assessment. Plasma cfDNA integrity index was calculated as the ratio of long to short DNA fragments (ALU 247/115) amplified and detected by real-time PCR. Serum CEA and CA19-9 were measured by chemiluminescent immunometric assay. RESULTS: Baseline cfDNA integrity index was statistically significantly different between responders and non-responders (p=0.03). It was found that at cut off 0.608, sensitivity was 73.7%, specificity was 66.7% and diagnostic accuracy=69.77%. Markers with statistical significant difference between responders and non-responders after chemotherapy were CEA % change (p=0.035), CA19-9 (p=0.024), cfDNA integrity index (p=0.035) and cfDNA integrity index % change (p<0.001). Among these markers, cfDNA integrity index % change had the best sensitivity (84.2%), specificity (95.2%) and diagnostic accuracy (90.7%) at cut off -17.827%. CONCLUSION: Baseline cfDNA integrity index can be used as a potential marker to predict response to chemotherapy. cfDNA integrity index (ALU 247/115) % change rather than its absolute value is superior to CEA, CA19-9, cfDNA concentration and their % changes in early assessment of response to chemotherapy.