Maryam Doroudi

PhD MPH

National Cancer Institute

Cancer Prevention Fellow

PLCO (Learn more about this study)

PLCO-176

Nov 4, 2015

Flexible Sigmoidoscopy in the Randomized Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial: Colorectal Cancer Survival by Trial Arm

In the United States and the United Kingdom, screening with flexible sigmoidoscopy is associated with a significant reduction in CRC-specific mortality and incidence. However, it is not clear what fraction of the observed mortality reduction is actually due to early detection of CRC, as opposed to its prevention via removal of adenomatous polyps. Using cancer survival statistics to assess the effectiveness of screening is well-known to be problematic, due to the potential biases of lead-time and over-diagnosis. Owing to these biases, a population undergoing screening may have a better observed survival rate than a similar population which is not undergoing screening. However, this does not necessarily imply a mortality reduction of the cancer of interest in the screened population due to the above biases. Lead-time and over-diagnosis can cause survival rates to improve even with no decrease in mortality. However, the converse statement may well be true; that is, if survival is not improved, then mortality rates cannot be decreased. Consequently, if survival is not better for the screened arm CRC cases than the control arm CRC cases, the early detection per se (as opposed to prevention of CRC in the first place), likely, cannot be contributing to the mortality reduction. Using PLCO trial data, we plan to investigate the association between survival (all-cause survival and CRC-specific survival) and trial arm, and CRC stage and trial arm.

We propose to examine the following specific aims using data from the PLCO trial:

Specific Aim 1: Assess whether there are differences in all-cause survival or CRC-specific survival by trial arm. Our working hypothesis is that there are no differences in all-cause survival or CRC-specific survival by trial arm.

Specific Aim 2: Assess whether there are differences in CRC tumor stage distribution by trial arm. Our working hypothesis is that there are no differences in tumor stage distribution by trial arm.