Introduction Cancer cachexia is a multifactorial syndrome characterized by persistent skeletal muscle loss and poor prognosis in cancer patients. Anamorelin, a ghrelin receptor agonist, may alleviate cachexia symptoms by increasing appetite and promoting weight gain, though its clinical efficacy remains insufficiently explored. Given the involvement of cancer-inducing cytokines in cachexia, the neutrophil-to-lymphocyte ratio (NLR), an inflammatory biomarker, may serve as a predictor of therapeutic outcomes in this condition. This study aimed to evaluate the role of NLR in assessing the therapeutic effects of anamorelin and its prognostic value in patients with cancer cachexia. Methods This study included patients with cancer cachexia associated with pancreatic, non-small cell lung, gastric, or colorectal cancer who received anamorelin between April 2021 and December 2023. Patients were categorized based on their NLR (<
5 or ≥5) at four weeks post-anamorelin administration. Changes in NLR and one-year overall survival (OS) rates were compared between groups. Baseline NLR was also assessed for its impact on survival outcomes. Statistical analyses included the Kaplan-Meier method for survival analysis, and receiver operating characteristic (ROC) analysis was used to determine the optimal baseline NLR cutoff for achieving a posttreatment NLR <
5. Results Of the 66 patients who received anamorelin, 42 had pancreatic cancer, 14 had non-small cell lung cancer, 6 had gastric cancer, and 4 had colorectal cancer. Patients were stratified into two groups based on their NLR at four weeks: NLR <
5 (n = 50, 76%) and NLR ≥ 5 (n = 16, 24%). In the NLR <
5 group, the mean NLR decreased significantly from 3.71 to 2.44, while in the NLR ≥ 5 group, it increased from 5.70 to 9.52. The one-year OS was significantly higher in the NLR <
5 group (62%, n = 31/50) compared to the NLR ≥ 5 group (33%, n = 5/16). Baseline NLR classification, however, showed no significant survival difference between the baseline NLR <
5 group (58%, n = 21/51) and the NLR ≥ 5 group (41%, n = 6/15). ROC analysis identified a baseline NLR <
4.4 as predictive of achieving a posttreatment NLR <
5 (AUC, 0.78
sensitivity, 80%
specificity, 75%), with significantly higher one-year OS observed in the baseline NLR <
4.4 group (68%, n = 29/42) compared to the NLR ≥ 4.4 group (34%, n = 8/24). Conclusions These findings highlight the potential of NLR as a prognostic marker and suggest that initiating anamorelin treatment with a baseline NLR <
4.4 is likely to improve outcomes, emphasizing the importance of NLR-based therapeutic interventions.