IntroductionThe current study aimed to evaluate the ability of a modified version of the age-adjusted Charlson Comorbidity Index (mACCI) in predicting cause-specific survival (CSS) among patients with gastric cancer who underwent curative gastrectomy and compared it with the conventional ACCI. Materials and methodsPatients who underwent gastrectomy for gastric cancer from 2007 to 2016 (n = 2885) were included. A mACCI was established by excluding scores for other malignancies, such as other cancers, leukemia, and lymphoma. After determining the optimal cutoff ACCI and mACCI values for CSS, clinicopathological factors and survival outcomes were assessed according to the ACCI and mACCI. ResultsBoth ACCI and mACCI were identified as independent prognostic factors for overall survival (p < 0.001 and p < 0.001, respectively). However, only mACCI was identified as an independent prognostic factor for CSS (p < 0.001). The present study suggested that mACCI was a better indicator of CSS in patients with gastric cancer who underwent curative gastrectomy than ACCI. ConclusionOur findings showed that the mACCI was a strong predictor of CSS in patients with gastric cancer who underwent curative gastrectomy. We believe that the mACCI will become a novel marker that would guide treatment decisions for patients with gastric cancer suffering from comorbidities.