Patients with inflammatory bowel disease (IBD) are at increased risk of developing colorectal cancer (CRC), particularly if presence of primary sclerosing cholangitis (PSC). We aim to characterize CRC in patients with PSC-IBD, including location and preceding endoscopic and histologic findings.

We performed a retrospective study from 154 patients with PSC-IBD (128 with ulcerative colitis, 26 with Crohn’s disease) and subsequent CRC diagnosis who were treated at Mayo Clinic between 1990 and 2023. Patients were identified using billing codes and natural language processing. We retrieved demographic data, IBD duration and disease activity based on endoscopic and histologic findings preceding CRC diagnosis. CRC location was divided into right (cecum, ascending colon, transverse colon) and left colon (descending colon, sigmoid colon, and rectum). Endoscopic scoring was assigned to each segment based on no inflammation (0), mild (1), moderate (2), and severe (3). Similarly, histologic scoring was assigned based on normal (0), quiescent (1), mild (2), moderate (3), and severe (4).  Average endoscopic and histologic scores of all colonic segments were obtained. Incidence of cholangiocarcinoma was also captured regardless prior or latter onset to CRC diagnosis. 

Age of onset in PSC-IBD patients was 66.32±14.9. CRC presented as a single lesion in 128 patients (33 CRCs presented in the cecum, 46 in the ascending colon, 19 in transverse colon, 7 in descending, 8 in sigmoid, and 15 in rectum) versus 10 synchronous CRCs (major incidence in ascending/transverse with 4 cases). Sixteen patients had CRC of unknown location. Synchronous CRCs presented in younger patients (55.7±15 vs 65.3±14.3; p-value=0.047) compared to single CRCs but there was no significant difference in IBD duration at CRC onset (21.1±6.9 vs 20.5±10.6; p-value=0.87). There was no significant difference in right CRCs age of onset (51±12.18 vs 46.8±10.7; p-value=0.19), IBD duration at CRC onset (21.2±11.4 vs 18.44±8.45; p-value=0.27) when compared to left CRCs. Left CRC incidence was higher in patients with CRC onset before the age of 60 (28% vs 11.4%; p-value 0.04). There was no significant difference in cholangiocarcinoma onset between right and left CRCs. Interestingly, when comparing among colonic segments, cholangiocarcinoma diagnosis preceded cecal (n=6) and descending CRCs (n=2) by 11.4±10.8 and 19±9.9 years (p-value=0.006) respectively while the rest of segments presented either at time of or after CRC diagnosis. Average endoscopic and histologic scores were not significant different between right and left CRCs at the time of diagnosis.

Despite PSC-IBD patients are more likely to present with right CRCs, patients younger than 60 have a higher incidence of left CRCs when compared to the older counterpart. It was also noted that synchrounous CRCs present at a younger age. It is well known that IBD duration is a risk factor for CRC development but pathogenesis is likely multifactorial. Future studies are needed to determine other risk factors, such as genetic variants, in PSC-IBD CRCs.