Association of Proteinuria as an Observed Side Effect with a Worsening Rate of Renal Function Decline in Patients with Colorectal Cancer Treated with Bevacizumab

The effect of proteinuria, a side effect of bevacizumab (BV) treatment, on the subsequent rate of renal function decline in patients with colorectal cancer remains inconclusive. In this study, we conducted a retrospective cohort study of 204 patients with colorectal cancer aged 18 years or older who received BV at Kanazawa Medical University Hospital from January 2014 to October 2024. The patients were classified into 2 groups based on the highest urine protein test values after the start of BV administration: a proteinuria-positive group (urinary protein test 2+ or higher) and a proteinuria-negative group (urinary protein test <1+). The rate of decline in renal function (i.e., estimated glomerular filtration rate [eGFR] slope) from the start of BV to 2 months after completion of BV was compared between the 2 groups using generalized estimating equations. In a model adjusted for confounding factors such as baseline renal function, age, sex, use of drugs or diabetes medications affecting renal function, and total dose of BV, the rate of decline in renal function was significantly greater in the proteinuria-positive group compared with the proteinuria-negative group (eGFR slope in mL/min/1.73 m²/year: proteinuria-positive group: -2.80 [95% confidence interval, CI: -5.38 to -0.23]; proteinuria-negative group: -0.13 [95% CI: -2.55 to 2.28], p = 0.03). These results suggest that proteinuria, a side effect of BV treatment, is associated with a subsequent worsening rate of renal function decline in patients with colorectal cancer.