Patients who delayed getting colonoscopies longer than 6 months after a positive fecal immunochemical test (FIT) showed significantly greater risks of being diagnosed with colorectal cancer when they finally did have the procedures, a researcher said here.
But the groups at highest risk were not those that might have been expected, according to Douglas Corley, MD, PhD, of Kaiser Permanente’s research division in Oakland, Calif., who reported the study at Digestive Disease Week (DDW).
Among some 71,000 Kaiser Permanente members who underwent colonoscopies after positive FIT, those who had the procedures after 6-12 months were at significantly increased risk of a colorectal cancer diagnosis (odds ratio 1.3, P<0.05) relative to those having colonoscopies within 30 days of the positive FIT (considered no delay).
Those undergoing colonoscopies beyond 1 year were at even greater risk, Corley said, with an OR of 2.4 (P<0.05) relative to the group with no delay.
The increased risk with delayed colonoscopy were mainly reflected in advanced-stage disease, he stated. In those undergoing colonoscopies more than a year after positive FIT, the ORs for diagnosis with stage III and IV cancers were 2.6 and 4.3, respectively, relative to the no-delay group.
John Vargo, MD, MPH, of the Cleveland Clinic, who was not involved with the study, said it was among the most important presented at DDW this year on colorectal cancer detection and prevention.
He said it confirmed what is usually believed: “earlier is better” when it comes to diagnosing colorectal cancer in high-risk patients.
Corley said his group went into the study with a number of hypotheses about the reasons for delay and how they might be reflected in cancer diagnoses. One was that individuals with multiple comorbidities would be more inclined to delay having a colonoscopy, and would therefore be more likely to be diagnosed with cancer.
But in fact the researchers found the opposite: when long delays occurred, the highest risks were in individuals with few comorbid conditions. In some cases, the increase in risk was enormous.
For diagnosis of colorectal cancer among those with Charlson comorbidity scores of 2 or more, risks were about the same irrespective of time between FIT and colonoscopy, even when it went beyond a year. For those with Charlson scores of 0 or 1, however, the OR reached 5 for those ages 50-60 and almost 14 for those ages 61-75 when colonoscopy occurred more than a year after FIT relative to the no-delay group.
The same pattern, but magnified, was seen for advanced cancers. Delays of a year or more were associated with OR of 25 at ages 50-60 and OR 45 at ages 61-75 (all P<0.05).
“We don’t have a complete explanation” for these subgroup results, Corley said.
Other potential confounders for which the group had data — sex, body mass index, race/ethnicity, previous FIT history, or screening year — did not affect the results. Nor did the patterns change when the reference group was expanded to include those having colonoscopies up to 90 days after FIT.
Asked during the question period about the factors underlying the delays, Corley responded that this was not practical to address in the study. But, he added, in his “personal experience,” there numerous reasons for patients to wait to have colonoscopies.
Some may have difficulty getting time off from work; or a patient may be having coronary interventions and needs to “come off Plavix” before undergoing another procedure.
“It’s kind of a hodgepodge of things,” he said.