Tumor-Infiltrating Lymphocytes as Mediators of the Obesity and Papillary Thyroid Carcinoma Lymph Node Metastasis Association: An Observational Retrospective Cohort Study

Background: Obesity increases the risk of papillary thyroid carcinoma (PTC) and lymph node metastasis (LNM), possibly via modulation of the tumor immunological microenvironment. Materials and methods: The STROCSS guideline was followed to conduct a retrospective cohort study. Binary logistic regression analysis with odds ratios (OR) was performed to assess the association between tumor-infiltrating lymphocytes (TILs), obesity, and LNM. Using The Cancer Genome Atlas (TCGA) data, we examined the relationship between immune cell subsets and obesity-regulating molecules in thyroid cancer tissues. The Cox regression risk model was used to analyze the prognosis of thyroid cancer. Results: After adjusting for confounding factors, our findings revealed that overweight and obesity were associated with a decrease in TIL infiltration (OR 0.876, p = 0.005 and OR 0.795, p = 0.001, respectively). Furthermore, these conditions were observed to be correlated with increased likelihood of LNM (OR 1.134, p = 0.005 and OR 1.307, p < 0.001, respectively). On the contrary, TIL infiltration was inversely associated with LNM (OR 0.868, p < 0.001). When controlling for TIL infiltration as the sole variable, the combination of obesity and TIL infiltration did not independently predict LNM (adjusted OR 1.442, p = 0.113). However, obesity alone was found to elevate the likelihood of LNM (adjusted OR 1.539, p = 0.02). Additionally, adiponectin (a crucial adipokine) was reduced in obesity and demonstrated a negative correlation with the abundance of infiltrated dendritic cells and regulatory T cells, as evidenced by TCGA data analysis. Furthermore, ADIPOR2 expression negatively correlated with LNM and positively associated with unfavorable prognosis in PTC, with a hazard ratio of 0.480 (p = 0.007). Conclusions: TIL infiltration may affect obesity-associated PTC LNM. Obesity may affect LNM and result in poor prognosis through ADIPOR2 regulation of antitumor immune cells.