Objective: To investigate the prevalence of thyroid cancer (TC) in patients with type 2 diabetes mellitus (T2DM) and the relevant risk factors.   
Methods: A total of 1 662 T2DM patients (T2DM group) hospitalized from June 2016 to December 2018, and 604 subjects (control group) undergoing health maintenance examination and with exclusion of diabetes during the same period were enrolled. The prevalence rates of TC between the two groups were compared, and the relevant variables between T2DM patients with and without TC were also compared.
Results: In T2DM group, the prevalence rate of TC was higher than that in control group (7.46% vs. 1.32%), which was also higher in female patients than that in male patients (54.0% vs. 46.0%) and higher in patients ≥45 years than that in those <45 years (77.4% vs. 22.6%), and all differences had statistical significance (all P<0.05). The percentage of postoperatively diagnosed TC in the same TI-RADS classification in T2DM group showed an increasing trend compared to control group (effective statistical analysis could not be performed due to the extremely small sample number in the control group). In T2DM group the body mass index and levels of fasting blood glucose, postprandial 2-h blood glucose, glycosylated hemoglobin, thyroid stimulating hormone, triglyceride, neuron-specific enolase and cytokeratin 19 fragment in patients with TC were significantly higher than those in patients without TC (all P<0.05). All tumors in the 124 cases of the T2DM group were classified as papillary carcinoma.
Conclusion: The risk of TC is significantly increased in patients with T2DM, especially in female patients and those ≥45 years. Good blood glucose and lipid control, and maintenance of thyroid function within normal range in T2DM patients may have certain significance for the prevention of TC. Regular thyroid B-ultrasound examination is recommended in patients with T2DM.