# Screening Implications for Distribution of Colorectal Cancer Subsite by Age and Role of Flexible Sigmoidoscopy

## TL;DR

This study shows that flexible sigmoidoscopy can detect most colorectal cancers, especially in younger patients, and may be a good alternative to colonoscopy for screening.

## Contribution

The study provides evidence that flexible sigmoidoscopy can detect a high proportion of colorectal cancers, particularly in younger individuals.

## Key findings

- 58% of colorectal cancers are located in areas visible by flexible sigmoidoscopy.
- 73% of tumors in patients under 50 are detectable with sigmoidoscopy.
- Sigmoidoscopy may be a viable screening option for younger patients who avoid colonoscopy.

## Abstract

There is controversy over the optimal recommended screening practice for colorectal cancer. Between direct visualization methods, colonoscopy is more used more frequently, although randomized data suggest benefits from sigmoidoscopy rather than colonoscopy. We used the SEER database to assess the proportion of cancers that could be visualized with each screening strategy and found that 58% could be seen by sigmoidoscopy, including 73% of tumors for patients diagnosed younger than 50 years (early onset colorectal cancer). We recommend consideration of recommending flexible sigmoidoscopy as a population-based screening strategy for younger individuals who may be hesitant to undergo colonoscopy.

Objectives: The effectiveness of colonoscopy to reduce colorectal cancer (CRC) mortality is extrapolated from cohort studies in the absence of randomized controlled trial (RCT) data, whereas flexible sigmoidoscopy is supported by RCT data and may be easier to implement in practice. We characterized the anatomic distribution of CRC to determine the proportion that is visible with sigmoidoscopy. Methods: Patients with a primary diagnosis of colorectal adenocarcinoma were identified in the Surveillance, Epidemiology, and End Results program (2000–2020). Tumors from the rectum to the descending colon were categorized as visible by sigmoidoscopy, whereas more proximal tumors required colonoscopy. Differential prognosis between tumor locations, stratified by age groups and stage, was assessed using the overall restricted mean survival time (RMST) at 2, 5, and 10 years. Results: Among 309,466 patients, 58% had tumors visible by sigmoidoscopy, including 73% of those under age 50 (OR 2.10, 95% CI 2.03–2.16 age < 45, OR 2.20, 95% CI 2.13–2.27 age 45–49 versus age ≥ 50). Male sex (OR 1.54, 95% CI 1.51–1.56) and Asian or Pacific Islander race (OR 1.60, 95% CI 1.56–1.64) were also positively associated with tumors visualizable by sigmoidoscopy. Across age groups, for local disease, RMST was comparable for tumors visible versus not visible on sigmoidoscopy. For regional and metastatic cancer, patients with tumors visible by sigmoidoscopy had improved RMST versus those with more proximal tumors. Conclusions: 58% of CRC arises in locations visible by flexible sigmoidoscopy. Flexible sigmoidoscopy should be considered as a viable option for CRC screening, particularly in younger patients unwilling or unable to undergo colonoscopy.