Later follow-up colonoscopy equals higher colorectalcancer risk

Patients who undergo follow-up colonoscopy 10 months or more after a positive fecal immunochemical test are at higher risk for colorectal cancer and for more advanced disease at diagnosis, than are those who undergo immediate (within 30 days) follow-up colonoscopy, according to a new report. Clinical practice guidelines recommend follow-up colonoscopy after a positive fecal immunochemical test (FIT) result but differ about how quickly the procedure should be done, chiefly because there is little evidence on which to base any recommendation regarding timing, reported  at Kaiser Permanente Northern California, Oakland, and his associates.

To examine whether the length of the interval between FIT testing and colonoscopy affected diagnosis, they analyzed clinical data for 70,124 adults aged 50-75 years who were members of two large health organizations and who completed FIT testing during a three-year period. The investigators compared outcomes among the 27,176 patients who had follow-up colonoscopy within 30 days (the reference group) against those of patients who had follow-up colonoscopy after two months (24,644 patients), three months (8,666 patients), 4-6 months (5,251 patients), 7-9 months (1,335 patients), 10-12 months (748 patients), or more than 12 months (2,304 patients).

A total of 2,191 colorectal cancers were diagnosed at follow-up colonoscopy, including 601 cases of advanced disease, the investigators reported.

There was no significant increase in risk for any colorectal cancer among patients who had follow-up colonoscopy within nine months, compared with the reference group. However, the risks of any colorectal cancer and of advanced colorectal cancer increased significantly at 10 months (odds ratios, 1.48, 1.97).

The risks continued to rise as the interval between testing and colonoscopy lengthened, so that, after one year, the odds ratios were 2.25 for any colorectal cancer and 3.22 for advanced-stage disease. After one year, the odds ratios were 1.32 for advanced adenomas, 2.94 for stage IV colorectal cancer.

The National Cancer Institute supported the study.