Objective & method: A dimeric form of pyruvate kinase isoenzyme (tumour M2-PK) is predominantly found in highly proliferating cells. Sandwich ELISA with monoclonal antibodies against dimeric (tumour) M2-PK was used to measure faecal tumour M2-PK in; 13 controls, 10 patients with colonic polyps and 32 patients with colorectal cancer.
Results: Levels of faecal tumour M2-PK were higher in patients with colorectal cancer (median 11.72 U/ml; range 0.9-146.95 U/ml, P = 0.0001) and polyps greater than 10 mm (median 2.54 U/ml; range 0.9-29.46 U/ml, P = 0.041) when compared with controls (median 1.75 U/ml; range 0.9-3.41 U/ml). Furthermore, levels were higher in stages Duke's B (P = 0.013) and Duke's C (P = 0.43) than in Duke's A. Six months postsurgery faecal tumour M2-PK levels fell significantly to 3.46 U/ml (range 1.03-9.05 U/ml, P = 0.001). The sensitivity of a positive faecal tumour M2-PK test, defined as a level above 3.33 U/ml, was 91% for colorectal cancer, 60% for >10 mm and 20% for <10 mm polyps, with a specificity of 92%.
Conclusion: Faecal tumour M2-PK is a highly sensitive marker for colorectal cancer and larger polyps. It also correlates with more advanced stages of colorectal cancer and its reduction is associated with successful surgical intervention.