Overall mortality in men and women in the randomized Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

Objective

To assess the secondary outcome of overall mortality in the randomized Prostate, Lung, Colorectal, and Ovarian cancer screening trial.

Methods

In the Prostate, Lung, Colorectal, and Ovarian trial, subjects were randomized to usual care or intervention. In the intervention arm, men and women received annual chest radiographs and two sigmoidoscopy exams. Men also received annual prostate-specific antigen tests and digital rectal exams, and women also received annual CA125 tests and trans-vaginal ultrasounds. Poisson regression and Cox proportional hazards models were used to assess differences across trial arms in overall mortality and overall mortality excluding deaths from trial cancers (OMEX). Due to slight age imbalances in later trial years, age-adjusted rate ratios and hazard ratios were computed.

Results

There were 76,678 men and 78,209 women randomized, with median follow-up of 17 years. In men there was a significant reduction in both overall mortality (age-adjusted rate ratio = 0.966; 95% CI: 0.943–0.989; p = 0.004) and OMEX (age-adjusted rate ratio = 0.970, 95% CI: 0.946–0.995; p = 0.02) in the intervention versus usual care arm. In women, no reduction was seen in either overall mortality (age-adjusted rate ratio = 1.002) or OMEX (age-adjusted rate ratio = 1.006). In both sexes combined, there was a significant reduction in overall mortality (age-adjusted rate ratio = 0.980; 95% CI: 0.963–0.999; p = 0.036) but not OMEX (age-adjusted rate ratio = 0.985; 95% CI: 0.965–1.004; p = 0.13). Results were similar using age-adjusted hazard ratios.

Conclusion

In the Prostate, Lung, Colorectal, and Ovarian trial, there was a small but significant reduction in overall mortality in men, and in both sexes combined, and a small but significant reduction in overall mortality excluding trial cancer deaths in men.

Considerations in the design of randomized trials to screen for type 2 diabetes

Background Randomized controlled trials (RCTs) are the most robust and valid approach to evaluate screening for diseases. Many in the diabetes research community have advocated sole reliance on RCTs for designing diabetes screening policies. However, the challenges of conducting RCTs of screening for type 2 diabetes may have been underappreciated. Purpose Discuss the key theoretical concepts and practical challenges of designing and conducting RCTs of diabetes screening. Methods Narrative and critical review of the literature pertaining to the theory and practice of designing and conducting RCTs of diabetes screening. Results We present the theoretical basis of a diabetes screening trial, using concepts developed mainly in studies of cancer screening and illustrations from the Cambridge component of the Anglo Danish Dutch Study of Intensive Treatment In peOple with screeN-detected diabetes in primary care (ADDITION-Cambridge), the only extant trial of diabetes screening. We examine design issues, including the appropriate trial question, choice of design, and duration of follow-up, and address aspects of trial implementation, including recruitment, randomization, endpoint determination, sample size requirements, and screening interval. Limitations The limited number of trials of diabetes screening did not permit us to illustrate many of the practical difficulties one encounters when implementing theoretical concepts. Conclusion When diabetes screening trials are planned, we suggest careful consideration to potential areas of practical difficulty, especially the need for particularly large sample sizes and extended follow-up, and the choice of appropriate outcomes and screening intervals.

A note on the design of cancer screening trials

OBJECTIVES

To investigate the consequences of different cancer screening trial designs and follow-up options for accuracy of the estimate of the effect of screening on disease-specific mortality.

METHODS

We consider a randomized trial of breast cancer screening with a screening phase in which the intervention group is offered screening and the control group is not, and optional further follow-up after this screening phase. Postulating a lead time effect similar to that observed in breast cancer screening trials, we calculate the observed relative risk of disease-specific mortality and compare this with the true relative risk, for four design options: (1) no follow-up beyond the screening phase, ie. the screening phase and the observation period are identical; (2) follow-up continuing beyond the screening phase, all cancer-specific deaths counted, including those diagnosed after the screening phase; (3) follow-up continuing beyond the screening phase, but with only deaths from cancers diagnosed during the screening phase included; and (4) follow-up continuing beyond the screening phase, a single screen of the control group conducted at the end of the screening phase, and only deaths from cancers diagnosed during the screening phase in both arms up to completion of the single control screen included.

RESULTS

All designs in which follow-up for mortality continues beyond the screening phase incurred a bias against screening. The design in which the control group undergoes a single screen at the end of the screening phase was least biased in the example used.

CONCLUSIONS

The expedient of a single screen of the control group at the end of the screening phase has acceptable accuracy, but is still slightly conservatively biased.