High Tumour Cannabinoid CB1 Receptor Immunoreactivity Negatively Impacts Disease-Specific Survival in Stage II Microsatellite Stable Colorectal Cancer

Background There is good evidence in the literature that the cannabinoid system is disturbed in colorectal cancer. In the present study, we have investigated whether CB 1 receptor immunoreactive intensity (CB 1 IR intensity) is associated with disease severity and outcome. Methodology/Principal Findings CB 1 IR was assessed in formalin-fixed, paraffin-embedded specimens collected with a consecutive intent during primary tumour surgical resection from a series of cases diagnosed with colorectal cancer. Tumour centre (n = 483) and invasive front (n = 486) CB 1 IR was scored from 0 (absent) to 3 (intense staining) and the data was analysed as a median split i.e. CB 1 IR <2 and ≥2. In microsatellite stable, but not microsatellite instable tumours (as adjudged on the basis of immunohistochemical determination of four mismatch repair proteins), there was a significant positive association of the tumour grade with the CB 1 IR intensity. The difference between the microsatellite stable and instable tumours for this association of CB 1 IR was related to the CpG island methylation status of the cases. Cox proportional hazards regression analyses indicated a significant contribution of CB 1 IR to disease-specific survival in the microsatellite stable tumours when adjusting for tumour stage. For the cases with stage II microsatellite stable tumours, there was a significant effect of both tumour centre and front CB 1 IR upon disease specific survival. The 5 year probabilities of event-free survival were: 85±5 and 66±8%; tumour interior, 86±4% and 63±8% for the CB 1 IR<2 and CB 1 IR≥2 groups, respectively. Conclusions/Significance The level of CB 1 receptor expression in colorectal cancer is associated with the tumour grade in a manner dependent upon the degree of CpG hypermethylation. A high CB 1 IR is indicative of a poorer prognosis in stage II microsatellite stable tumour patients.