Tumor M2PK vs. FIT Tests



Introduction Faecal immunochemical tests (FIT) are acceptable to a large part of the general population but used alone are poor at detecting adenomas. An ELISA which measures faecal M2-pyruvate kinase (M2-PK) has been shown to be useful for detecting colonic pathology. 

Aims To prospectively compare M2-PK and FIT in screening for colonic polyps and cancer in the second round of our pilot FIT-based Colorectal cancer screening programme. 

Methods The second round of our FIT pilot programme was conducted over a two year period. Patients were sent invites by post to return a FIT sample from each of two days. All participants were aged 50 – 74 and living locally to our hospital. As part of this round, over a six month period all invitations additionally included containers to collect a single M2-PK stool sample. All FIT’s returned on time were measured locally. All M2-PK samples received within 48 hours of passing stool were frozen and analysed centrally by ScheBo Biotech AG (Germany). 

All FIT positive (>100 ngHb/ml) or M2-PK positive (>4 U/ml) patients were contacted and assessed for colonoscopy. All colonoscopies were conducted in the same way between both groups. 

Results Over the six month period 1,800 combined M2-PK and FIT invites have been sent. 

879 samples were returned and analysed for faecal M2-PK and FIT; of these 245 were positive for either one or both of these markers. After being contacted 34 (13%) of this group were excluded as they had a colonoscopy within 3 years and were all in polyp surveillance programmes. 

Of the remaining patients: 30 (3.4% of 879) were FIT positive M2-PK negative; 160 (18.2%) were positive for M2-PK ( > 4U/ml) negative for FIT and 21 (2.3%) were positive for both markers.

In the FIT positive M2-PK negative group there were 10 patients with adenomas (adenoma detection rate 33%). In those who were M2-PK positive but FIT negative there were 34 people with adenomas (ADR 23%). Therefore these adenomas would not have been detected by relying on FIT alone. Of the remaining 21 positive for both, 6 (29%) had adenomas and another 4 (19%) had colitis/proctitis. There have not been any cancers in this group to date. 

Interestingly sessile serrated adenomas were detected in 5 (4.4%) of people M2-PK positive but only two (less than 1%) in our entire FIT positive group. 

Conclusion Studies have shown FIT has relatively low sensitivity for adenomas. The addition of another stool marker such as faecal M2-PK increases the detection of polyps in a screening population. A single M2-PK sample detects more adenomas than two day FIT alone. Also M2-PK appears to be more sensitive for serrated adenomas than FIT but further studies are needed to confirm this.