Impact of the serum creatinine and cystatin C ratio for prediction of sarcopenia and prognosis in biliary tract cancer

Background Sarcopenia is a poor prognostic factor in cancer patients. In recent years, there have been reports that serum creatinine and cystatin C (Cr/CysC) ratio is associated with sarcopenia. However, the prognostic value of the Cr/CysC ratio in biliary tract cancer is unclear. We evaluated the impact of the Cr/CysC ratio on sarcopenia and prognosis in biliary tract cancer. Methods We retrospectively reviewed the records of 190 patients with biliary tract cancer who had undergone surgical resection from January 2017 to March 2023. Frozen serum samples collected at the time of surgery were used to measure CysC. We calculated the Cr/CysC ratio and investigated the relationship with sarcopenia and the prognostic significance. Results We calculated the cutoff value of the Cr/CysC ratio for low skeletal muscle index (SMI) (< 42 cm(2)/m(2) for males and < 38 cm(2)/m(2) for females). The optimal cutoff value of the Cr/CysC ratio was 0.848. The low Cr/CysC ratio group was significantly associated with higher preoperative CRP and lower albumin, lower SMI, lower handgrip strength, and higher intramuscular adipose tissue content. In multivariate analysis, patients with a low Cr/CysC ratio showed poorer overall survival (hazard ratio 2.60, 95% confidence interval 1.07-6.29, p = 0.033), which was significantly worse than in those with a high Cr/CysC ratio. Conclusions In patients with biliary tract cancer, the Cr/CysC ratio showed weak correlation with sarcopenic indicators. However, the Cr/CysC ratio could be strong prognostic factor in biliary tract cancer.