Investigating the causal relationship between 731 immune phenotypes and thyroid cancer risk: A bidirectional Mendelian randomization study

Previous studies have demonstrated a significant correlation between immune cells and thyroid cancer (TC). Nevertheless, there remains uncertainty regarding whether this association indicates a causal relationship. We performed a bidirectional Mendelian randomization (MR) analysis to explore the causal relationship between 731 immune phenotypes and thyroid cancer. Our primary analytical method was the inverse variance weighting technique, complemented by supporting analyses using weighted median, MR-Egger, simple mode, and weighted mode. Our results were also robustly assessed using sensitivity analyses to account for heterogeneity and potential horizontal pleiotropy. The results from the inverse variance weighting analysis, which examined 7 groups of immune cells in their antithyroid cancer effects, indicated that 11 immune cell traits were positively correlated with the occurrence and progression of thyroid cancer (odds ratio [OR] > 1, P < .05), while 22 immune cell traits showed a negative correlation (OR < 1, P < .05). In the reverse MR analysis, thyroid cancer was positively associated with 2 immune cell phenotypes (P < .05, OR > 1) and negatively associated with 1 immune cell phenotype (P < .05, OR < 1). None of these findings displayed evidence of heterogeneity, horizontal pleiotropy, or reverse causality (P > .05). This research offers a perspective on the biological mechanisms between thyroid cancer and immune cells, contributing to the exploration of early intervention and treatment options.