Purpose <p>This study investigated the association between anamorelin (ANAM) treatment and longitudinal changes in renal function in patients with cancer cachexia.</p> Methods <p>This retrospective, single-centre, observational cohort study reviewed electronic medical records of patients diagnosed with cancer cachexia. Renal function parameters—including blood urea nitrogen (BUN), serum creatinine, and estimated glomerular filtration rate (eGFR)—were compared between patients treated with ANAM and those not receiving ANAM. Propensity score matching was applied to adjust for baseline imbalance in patient characteristics. Renal deterioration was defined as ≥ 10% increase in BUN or ≥ 10% serum creatinine, or ≥ 10% decrease in eGFR. Cox proportional hazards models were applied to BUN, serum creatinine, and eGFR deterioration, respectively.</p> Results <p>After propensity score matching, ANAM treatment was associated with significantly greater improvements in serum creatinine and eGFR over an 8-week period compared with non-ANAM treatment. Multivariable Cox regression analyses demonstrated that ANAM use was independently associated with a reduction in risk of ≥ 10% increase in serum creatinine and ≥ 10% decrease in eGFR. Longitudinal analyses revealed improvements in renal function markers in the early phase after initiation of ANAM, followed by a gradual return toward baseline levels.</p> Conclusion <p>ANAM treatment was associated with improvements in renal function markers and a lower risk of renal function deterioration in patients with cancer cachexia. These findings suggest that ANAM may potentially confer renoprotective effects in addition to its established therapeutic benefits for cachexia.</p>