In 2021, the National Kidney Foundation and the American Society of Nephrology Task Force recommended that clinicians estimate GFR using an equation that incorporates both cystatin C and SCr assessments in patients with or at risk for kidney disease.21 This combined equation may be particularly important in patients with cancer who may have large discordance between eGFRcr and eGFRcys. The gene discussed is CST3; the disease is cancer.