Molecular Test Accurately Detects Colon Cancer

The stool DNA test works by finding signature genetic markers in stool samples mailed in by patients and a positive test would be followed by a colonoscopy to remove the polyps and prevent a subsequent cancer from forming.

The screening test was developed in a collaboration between Mayo Clinic (Rochester, MN, USA) and Exact Sciences Inc (Madison, WI, USA). It is highly accurate and significantly more sensitive than other noninvasive tests at detecting precancerous tumors such as adenomas and early-stage cancer. The scientists performed a blinded, multicenter, case-control study using archived stool samples collected in preservative buffer from 252 patients with colorectal cancer (CRC), 133 with adenomas equal to or greater than 1 cm, and 293 individuals with normal colonoscopy results acting as controls. The stool DNA (sDNA) test detects four methylated genes, a mutant form of the Kirsten rat sarcoma viral oncogene (KRAS), and as a reference value the α-actin gene, using quantitative, allele-specific, real-time target and signal amplification; it also quantifies hemoglobin.

The sDNA test identified 85% of patients with CRC and 54% of patients with adenomas equal to or greater than 1 cm with 90% specificity. The test had a high rate of detection for all nonmetastatic stages of CRC, with an aggregate 87% detection rate for CRC stages I-III. Detection rates increased with adenoma size: sensitivity was 64% for polyps larger than 1 cm, 77% for those larger than 2 cm, 86% for those larger than 3 cm, and 92% for those larger than four cm. The stool DNA test detected 87% of curable-stage colorectal cancer in nearly 400 cases. Importantly, detection sensitivity was not affected by tumor location or stage.

The authors concluded that early-stage CRC and large adenomas can be detected throughout the colorectum and with high levels of accuracy by the sDNA test. Neoplasm size, but not anatomical site, affected detection rates. Further studies are needed to validate the findings in a larger population and optimize the sDNA test. Stephen Thibodeau, PhD, a geneticist at Mayo Clinic, said, "These data illustrate the strength of the multimarker stool DNA test to the critical screening targets - precancers and early-stage cancer, and, importantly, this test appears to uniquely represent an accurate noninvasive approach to large polyp detection, which offers the promise of actually preventing cancers from developing." The study was available online since November 2011 in the journal Gastroenterology.

Related Links:
Mayo Clinic
Exact Sciences Inc.