Association of stromal tumor infiltrating lymphocytes and body mass index with prognosis in esophageal squamous cell carcinoma patients

Driven by BMI-related metabolic dysregulation and chronic inflammation that affect immune cell infiltration and function, the prognostic value of stromal tumor-infiltrating lymphocytes (sTIL) in esophageal squamous cell carcinoma (ESCC) may be influenced by body mass index (BMI). However, supporting evidence for this association remains limited. We analyzed 809 ESCC cases from Taixing, China (2010–2014), quantifying sTIL with an unsupervised algorithm. Using restricted cubic spline and Cox models, we evaluated the impact of sTIL on prognosis and assessed whether this impact differed by BMI. After a median follow-up of 2.42 years, 479 patients died from ESCC. sTIL exhibited an L-shaped association with ESCC prognosis (P-nonlinear = 0.013). Higher sTIL percentages were associated with better overall survival (OS), with an adjusted hazard ratio (HR) of 0.437 (95% confidence interval [CI]: 0.306–0.622) in the fourth quartile (Q4) of sTIL compared to the first quartile (Q1). Patients who were overweight or obese 10 years prior to ascertainment had more favorable OS than those who were underweight, with an adjusted HR of 0.549 (95% CI: 0.365–0.827). The adjusted HR for ESCC prognosis moderately decreased with elevated BMI levels (P-trend < 0.05). Although BMI 10 years prior to ascertainment appeared to modify the prognostic value of sTIL, the effect modification was not statistically significant (P-interaction = 0.935). BMI 10 years prior to ascertainment may have a modifying effect on the prognostic value of sTIL, although this interaction did not reach statistical significance. These findings support the potential development of sTIL- and BMI‐based prognostic stratification strategies for ESCC patients and contribute valuable evidence to ongoing research on BMI-related cancer prognosis and its clinical translation.