Studies have sought to assess the performance of various GFR equations in patients with cancer, recently including those incorporating both serum creatinine and cystatin C. The ASON Position Statement Committee conducted a systematic review to assess the accuracy of GFR estimating equations versus mGFR as determined through urinary or plasma clearance of an exogenous filtration marker.5 A total of 39 studies were included, and the total number of patients was 21,949 (19,025 with solid cancers, 1146 with hematologic cancers, and 1778 with unspecified malignancies). The gene discussed is CST3; the disease is cancer.