Being up to date on screening substantially reduced the risk of death from colorectal cancer (CRC) in retrospective findings from two U.S. healthcare systems that had high rates of screening uptake.

The authors, Chyke A. Doubeni, MD, MPH, of the University of Perelman School of Medicine of the University of Pennsylvania in Philadelphia, and colleagues reported that among 1,750 CRC deaths, 75.9% occurred in people who had rectifiable failures in the screening process -- especially lack of follow-up on abnormal findings -- and these lapses significantly increased the risk of CRC death. Fewer than a quarter of deaths occurred in individuals whose screening was up to date.

The study, published in Gastroenterology, showed that CRC death was associated with higher odds of failure to screen or failure to screen at appropriate intervals, for an odds ratio (OR) of 2.40 (95% CI 2.07-2.77), while failure to follow up on abnormal results correlated with an OR of 7.26 (95% CI 5.26-10.0).

"Our study points to the importance of getting screened on time, keeping up to date on screening, and ensuring that follow-up testing occurs when the test is abnormal or incomplete," Doubeni told MedPage Today.

The most lapses in the screening process were failure to ever screen or to screen at appropriate intervals. About 8% of deaths occurred in those who did not receive follow-up after an abnormal screen.

The researchers looked at patients ages 50 to 90 in the Kaiser Permanente systems of Northern and Southern California who died of CRC during 2006 to 2012 after being enrolled for at least 5 years before diagnosis. The patients were compared with a matched cohort of cancer-free patients. Tests included colonoscopy, sigmoidoscopy, barium enema, and both fecal occult blood (FOBT) and fecal immunochemical (FIT) tests received in the 10 years before diagnosis.

The average age of patients at diagnosis was 70, and 49.5% were female, 67.0% were non-Hispanic white, 12.0% were non-Hispanic black, 9.4% were Hispanic, and 8.9% were Asian-Pacific Islander.

Significantly, more than three-quarters of those considered to be dying from CRC had an identifiable screening failure, including failure to screen (n=591, 33.8%), inappropriate screening intervals (n=574, 32.8%), no surveillance (n=22, 1.3%), or lack of follow-up (n=141, 8.1%). Screening was up to date in 24.1% (n=422) as of the diagnosis date.

Among those with follow-up after an abnormal result, 103 had a positive FOBT, and of these, 58 (57.3%) had a documented order for diagnostic colonoscopy (n=42), sigmoidoscopy (n=14), or barium enema (n=2). Of patients with follow-up, 60 received further FOBT after an initial positive, six had only barium enema, and two had only sigmoidoscopy.

The majority of the tumors in patients who were up to date with screening by any test or indication were located in the right colon (61.8%, n=261), regardless of test type: colonoscopy (58.6%, n=41/70), sigmoidoscopy (68.5%, n=100/146), or fecal tests (58.6%, n=106/181). Failures to screen were more common in those with rectal or left colon cancers than those with right colon cancers (P=<0.01).

In patients with screening or follow-up failure, right colon cancers accounted for 45.3% (n=538) of all failures to screen combined, and 58.9% (n=83) of failures of follow-up. Failure to screen was associated with fewer visits to primary care physicians, suggesting that having a regular family doctor may affect participation.

In the 3,486 cancer-free controls, 44.6% were up to date on screening and these had a reduced risk of CRC death, with an odds ratio of 0.38 (95% CI 0.33-0.44).

Failure to screen or to screen at appropriate intervals was evident in 67.8% of patients who died from CRC versus 53.2% of cancer-free patients. Failure to follow up on abnormal results occurred in 8.1% of patients who died from CRC versus 2.2% of cancer-free patients.

In a community-based study, Doubeni's group had previously reported that 84% of the screening exposures in people who died of CRC occurred within 1 year of diagnosis, compared with 3% in matched cancer-free patients, suggesting that screening occurred too late in the disease course to be protective and reinforcing the potential benefits of timely initiation of screening.

Doubeni said that the 8% of individuals dying from CRC after an abnormal screening result without appropriate follow-up and the strong seven-fold association with mortality risk underscores the need for interventions to optimize the effectiveness of screening in preventing CRC deaths. A 2017 systematic review suggested that having patient navigators and sending providers reminders or performance data may improve follow-up after positive fecal tests, but evidence on effective system-level interventions is insufficient and this area needs further research. And a recent Kaiser Permanente study reported that directly mailing FIT kits to patients' homes modestly increased participation rates.

"Our study suggests that even in settings with high screening uptake, access to and timely uptake of screening, regular re-screening, appropriate use of testing given patient characteristics, completion of timely diagnostic testing when screening is positive, and improving the effectiveness of screening tests, particularly for right colon cancer, remain important areas of focus for further decreasing CRC death," Doubeni and associates wrote.