Risk of retinal vein occlusion in colorectal cancer patients receiving anti-vascular endothelial growth factors - a population-based cohort study

Anti-vascular endothelial growth factors (VEGFs) treatment has been associated with an increased risk of thromboembolic events. Therefore, the use of anti-VEGFs for patients with colorectal cancers (CRC) has raised concerns about the potential risk of retinal vein occlusion (RVO), an ocular disease caused by embolism or venous stasis. This study aims to evaluate the risk of RVO in patients with CRC treated with anti-VEGFs. We conducted a retrospective cohort study using the Taiwan Cancer Registry and National Health Insurance Database. The study cohort comprised patients newly diagnosed with CRC between 2011 and 2017, who received anti-VEGF treatment. For each patient in the study cohort, a control group comprising four patients newly diagnosed with CRC, but not receiving anti-VEGF treatment, was randomly selected. A washout period of 12 months was implemented to identify new cases. The index date was defined as the date of the first prescription of anti-VEGF drugs. The study outcome was the incidence of RVO, as identified by ICD-9-CM (362.35 and 362.36) or ICD-10-CM codes (H3481 and H3483). Patients were followed from their index date until the occurrence of RVO, death or the end of the study period. Covariates, including patients' age at index date, sex, calendar year of CRC diagnosis, stage of CRC and comorbidities related to RVO, were included. Multivariable Cox proportional hazards regression models were used to calculate hazard ratios (HRs) with adjustments for all covariates to compare the risk of RVO between the anti-VEGF and control groups. We recruited 6285 patients in the anti-VEGF group and 37,250 patients in the control group, with mean ages of 59.49 ± 12.11 and 63.88 ± 13.17 years, respectively. The incidence rates were 1.06 per 1000 person-years for the anti-VEGF group, and 0.63 per 1000 person-years for the controls. There was no statistically significant difference in RVO risk between the anti-VEGF and control groups (HR: 2.21, 95% CI: 0.87-5.61). Our results indicated no association between use of anti-VEGF and occurrence of RVO among CRC patients, although the crude incidence rate of RVO was higher in patients receiving anti-VEGF, compared to control patients. Future study with larger sample size is required to confirm our findings.