Power of screening tests for colorectal cancer enhanced by high levels of M2-PK in addition to FOBT

Colorectal cancer (CRC) is a multistep process that involves adenoma–carcinoma sequence. CRC can be prevented by routine screening, which can detect precancerous lesions. The aim of this study is to clarify whether faecal occult blood test (i-FOBT), tumor M2 pyruvate kinase (t-M2-PK), and endocannabinoid system molecules (cannabinoid receptors type 1—CB1, type 2—CB2, and fatty acid amide hydrolase—FAAH) might represent better diagnostic tools, alone or in combination, for an early diagnosis of CRC. An immunochemical FOB test (i-FOBT) and quantitative ELISA stool test for t-M2-PK were performed in 127 consecutive patients during a 12 month period. Endocannabinoid system molecules and t-M2-PK expression were detected by immunostaining in healthy tissues and normal mucosa surrounding adenomatous and cancerous colon lesions. i-FOBT and t-M2-PK combination leads to a better diagnostic accuracy for pre-neoplastic and neoplastic colon lesions. T-M2-PK quantification in stool samples and in biopsy samples (immunostaining) correlates with tumourigenesis stages. CB1 and CB2 are well expressed in healthy tissues, and their expression decreases in the presence of advanced stages of carcinogenesis and disappears in CRC. FAAH signal is well expressed in normal mucosa and low-risk adenoma, and increased in high-risk adenoma and carcinoma adjacent tissues. This study shows that high levels of t-M2-PK in addition to FOBT enhance the power of a CRC screening test. Endocannabinoid system molecule expression correlates with colon carcinogenesis stages. Developing future faecal tests for their quantification must be undertaken to obtain a more accurate early non-invasive diagnosis for CRC.