Introduction

Until now, there have only been conflicting reports regarding whether adenomas located proximal to the splenic flexure have increased association with metachronous colorectal cancer (CRC) compared to distal adenomas, and whether adenoma location should affect surveillance practice.

Aims & Methods

To address this knowledge gap, we aimed to compare metachronous colorectal cancer (CRC) and advanced adenoma (AA) risk in patients with baseline proximal vs. distal adenomas, including consideration of metachronous CRC location, baseline proximal adenomas only vs. both proximal and distal adenomas, and baseline proximal non-advanced adenoma vs. AA.
We systematically searched Pubmed, EMBASE, and Cochrane for cohort studies and clinical trials describing CRC or AA incidence at surveillance stratified according to baseline adenoma’s location. Proximal adenomas were defined as those located from the cecum to the splenic flexure. We performed a meta-analysis by calculating pooled incidence rate ratios (IRR) and corresponding 95% confidence intervals (CI) for CRC and AA using a random-effects model. Heterogeneity was assessed with the I2 statistic.

Results

The literature search yielded 5,907 studies of which 13 were included, with a total of 205,207 patients (mean age 62.3 years, 63.8% males) and a mean duration of follow-up of 8.5 years. Compared with patients with only distal adenomas, patients with any proximal adenoma and only proximal adenomas had a significantly higher risk of metachronous CRC [1.70 (95%CI: 1.17-2.46; I2=73%), and 1.97 (95%CI: 1.41-2.75; I2=0%)], respectively. Patients with any proximal AA had also a higher risk of CRC compared to those with only distal AA [2.77 (95%CI 1.77-4.34; I²=38%)]. Also, patients with any proximal adenoma had an even higher risk of proximal CRC compared to patients with baseline only distal lesions [3.65 (95%CI 1.57-8.47; I2=86%)]. Finally, patients with any baseline proximal adenoma had also a higher risk of metachronous AA [1.82 (95%CI: 1.41-2.34; I2=59%)].

Conclusion

Our findings suggest that baseline adenoma proximal location is associated with future detection of CRC and AA. Better understanding of the reasons behind this increased CRC risk, and particularly whether these can be overcome with improved colonoscopic technique or technical innovations, will inform whether baseline adenoma location should be considered in future guidelines as an independent factor to tailor surveillance recommendations.