Accurate glomerular filtration rate (GFR) evaluation is important in patients with cancer to determine correct dosing of chemotherapy and eligibility for treatments and clinical trials. Estimated GFR (eGFR) based on serum creatinine (Scr) (eGFRcr) using the 2009 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is recommended as the “initial test” for GFR evaluation for routine clinical practice in adults, and eGFR based on serum cystatin C (Scys), with or without Scr (eGFRcr-cys or eGFRcys, respectively) using the 2012 CKD-EPI equations or clearance measurements are recommended as confirmatory tests, as appropriate for the clinical setting.