Diagnostic value of pyruvate kinase isoenzyme type M2 in colon cancer proven with colonoscopy

Background: Colonoscopy is the gold standard for colon cancer screening; it is also associated with a high cost and complication. Proliferating cells, in particular tumor cells, express a dimeric isoenzyme of pyruvate kinase, termed M2 pyruvate kinase (M2-PK). The aim of this study was to determine the diagnostic accuracy of fecal M2-PK for colon cancer. Materials and Methods: Forty-nine patients with colon cancers and 49 healthy controls were selected consecutively among individuals undergoing screening colonoscopy for various indications. The diagnosis was confirmed by histology. M2-PK measurements were done by enzyme-linked immunosorbent assay of fecal occult blood test (FOBT) and immunological FOBT (IFOBT) according to the manufacturer's instructions. Results: M2-PK > 9 (U/mL) was the best cutoff point in the detection of colon cancers. In this cutoff point, sensitivity and specificity were 87.8% and 91.8%, respectively, and accuracy was 89.8%. The sensitivity and specificity of IFOBT were 93.9% and 100%, respectively, and accuracy was 96.9%. The sensitivity and specificity of FOBT were 65.3% and 100%, respectively, and accuracy was 82.6%. Conclusion: IFOBT with high sensitivity and specificity and accuracy and low cost is the best fecal screening test. The current study suggests that fecal M2-PK can be used for high-risk colon cancer patients and negative IFOBT that refused colonoscopy as a precolonoscopy screening test.