Gut microbiome versus thyroid cancer: Association and clinical implications (Review)

Thyroid cancer (TC) is one of the most prevalent endocrine tumors, and its incidence rates are increasing. Recent studies have shown that TC disrupts the gut microbiomes (GM) by influencing the levels of thyroid hormones, estrogen levels, weight and insulin resistance. Traditional treatments, including thyroid surgery, radioactive iodine (RAI) therapy and checkpoint inhibitors, also alter the GM. Additionally, GM affects the proliferation of TC by influencing chronic inflammation and metabolism (e.g., effects on short-chain fatty acids and amino acid metabolism). Notable changes in the GM of patients with TC include increased numbers of Clostridium, Streptococcus, Proteus and Lachnospiraceae, and decreased numbers of Lactobacillus, Prevotella and Ruminococcaceae bacteria. In addition, the GM may serve as a biomarker for diagnosis, prognosis and predicting metastasis in patients with TC, potentially enhancing diagnostic efficiency. Furthermore, the GM presents an opportunity to improve the efficacy of RAI therapy and immunotherapy in patients with TC. Probiotic combination approaches may also enhance clinical outcomes and the quality of life for individuals with TC. In conclusion, the present review discussed how there are bidirectional causal relationships between the GM and TC, emphasizing the role of the 'gut-thyroid' axis. Clostridium, Streptococcus, Proteus and Lachnospiraceae may be potential risk factors, whereas Lactobacillus, Prevotella and Ruminococcaceae may have protective roles for TC. Further investigations into macrobiotics-associated mechanisms should prove to be helpful in terms of optimizing strategies for the early prevention and treatment of TC.