# GFR Evaluation Among Patients with Cancer: Insights and Clinical Implications

## TL;DR

Accurate kidney function assessment is crucial for cancer patients, but traditional methods often fail due to cancer-specific physiological changes.

## Contribution

The paper emphasizes the need for updated GFR evaluation methods using newer equations and direct measurements in cancer patients.

## Key findings

- Traditional GFR equations like Cockcroft–Gault and MDRD are unreliable in cancer patients due to physiological changes.
- The CKD-EPI 2021 equation, which uses cystatin C and creatinine, improves GFR estimation accuracy in this population.
- Direct GFR measurement is recommended for high-risk cancer patients to ensure precise kidney function assessment.

## Abstract

Diagnosis of acute kidney dysfunction, adjusting lifesaving therapy dosing, or enrolling in cancer clinical trials are key elements in onconephrology, the overlap between cancer and kidney care. These elements primarily rely on an accurate assessment of kidney function in patients with cancer. Patients with cancer were excluded from deriving conventional kidney function estimating formulas, which often fail to provide a reliable estimate in malignancy. This is due to changes in muscle mass, body fluids, and how creatinine is excreted in cancer. These changes may lead to inaccurate kidney function assessments, impacting important treatment decisions and risk-averse events. Optimized approaches based on the most recent guidelines that utilize alternative kidney biomarkers, or direct measurement of kidney function, are warranted to improve care.

Accurately assessing the glomerular filtration rate (GFR) is critical in patients with cancer for acute kidney injury diagnosis, chemotherapy selection, drug dosing, and clinical trial eligibility. Yet, traditional equations such as Cockcroft–Gault and MDRD fail due to multiple physiological changes specific to this vulnerable population. Cancer-related sarcopenia, creatinine secretion blockade, and total body volume fluctuations may lead to inaccurate GFR estimations. This ultimately leads to undertreatment of underlying malignancy, overdosing of nephrotoxic therapies with adverse effects, and excluding patients from clinical trials unnecessarily. The 2024 KDIGO guidelines as well as the American Society of Onconephrology position statement recommend the use of combined GFR equation such as CKD-EPI 2021 that utilizes both cystatin C and creatinine to improve GFR estimation accuracy. Direct GFR measurement via exogenous filtration markers should be pursued in high-risk patients when precise values are warranted. This review highlights current challenges associated with GFR evaluation in patients with cancer and outlines clinical implications as well as recent recommendations for optimal clinical practice.