Pre-treatment serum bicarbonate predicts survival in patients with locally advanced esophageal squamous cell carcinoma undergoing definitive radiotherapy: a retrospective propensity score matching study

This study aimed to evaluate the prognostic value of pre-treatment serum bicarbonate (HCO 3 − ) for overall survival (OS) and progression-free survival (PFS) in locally advanced esophageal squamous cell carcinoma (LA-ESCC) patients undergoing definitive radiotherapy. Patients with stage Ⅱ-Ⅳ a ESCC treated with definitive radiotherapy between 2015 and 2022 were screened and then divided into Group A (high HCO 3 − ) and Group B (low HCO 3 − ). Propensity score matching (PSM) was performed using sex, age, ECOG score, body mass index, tumor length, tumor location, clinical T category, clinical N category, clinical TNM stage, combined chemotherapy, and radiation dose as covariates at a 1:2 ratio (Group A: Group B). OS and PFS were compared between different groups using Kaplan-Meier analysis and Cox regression analysis. A total of 301 patients were included in the study. The median follow-up time was 54.1 months. The median OS and PFS were 17.3 months and 11.0 months. The median HCO 3 − was 24.9 mmol/L. Before PSM, the median OS was 27.0 months in Group A (HCO 3 − ≥26 mmol/L, n = 103) and 14.8 months in Group B (HCO 3 − <26 mmol/L, n = 198), p < 0.0001. The median PFS was 16.3 months in Group A and 9.6 months in Group B, p = 0.0002. After 1:2 PSM, the median OS was 25.7 months in Group A ( n = 97) and 15.3 months in Group B ( n = 169), p = 0.0011. The median PFS was 13.0 months in Group A and 9.6 months in Group B, p = 0.0059. Multivariate Cox analysis suggested that age ≥ 66 (HR 0.739, p = 0.036), T category < 3 (HR 0.484, p < 0.001), clinical N category < 2 (HR 0.713, p = 0.022), combined chemotherapy (HR 0.625, p = 0.003), and HCO 3 − ≥26 mmol/L (HR 0.656, p = 0.004) were independent favorable prognostic factors for OS. Clinical T category < 3 (HR 0.565, p < 0.001), clinical stage Ⅱ-Ⅲ (HR 0.685, p = 0.019), and pre-treatment HCO 3 − ≥26 mmol/L (HR 0.717, p = 0.019) were independent favorable prognostic factors for PFS. A high pre-treatment serum bicarbonate level is associated with an increased OS and PFS in LA-ESCC patients undergoing definitive radiotherapy. Therefore, pre-treatment serum bicarbonate may serve as a readily available prognostic biomarker to inform risk stratification and treatment planning in LA-ESCC patients undergoing definitive radiotherapy.