Background and Aims: Thyroid cancer (TC) is not only one of the most common endocrine malignancies, but also has become the fastest growing cancer at present time. Diabetes mellitus (DM) is also currently one of the major global public health problems, and studies have demonstrated that DM is associated with the occurrence and development of various malignant tumors. This study was to investigate the clinicopathologic characteristics of patients with comorbid TC and DM by comparison with the clinicopathologic data and results of the thyroid B ultrasound of patients with TC alone, so as to provide reference for the treatment decision-making in patients with such condition. 
Methods: A total of 1 064 patients undergoing surgical treatment for TC from January 2016 to October 2019 in Xiangya Hospital of Central South University were enrolled. Of the patients, 245 cases had concomitant TC and DM (TC+DM group) and 819 cases had lone TC (TC group). And 604 subjects undergoing health maintenance examination during the same period in Xiangya Hospital of Central South University were also recruited (healthy control group). The differences in general features and biochemical parameters (DM-related indexes, thyroid function indexes and tumor markers) among TC+DM group, TC group and healthy control group were analyzed. The differences in clinicopathologic factors and thyroid ultrasound findings (TI-RADS) between TC+DM group and TC group as well as between groups with different glycated hemoglobin (HbA1c) levels in patients with comorbid TC and DM were compared.
Results: Compared with healthy control group, the female proportion, average age, and the levels of thyroid stimulating hormone and neuron-specific enolase in both TC+DM group and TC were significantly increased, and the increasing amplitudes in TC+DM group were significantly greater than those in TC group (all P<0.05); the BMI and DM-related indexes (fasting plasma glucose, 2-hour post-meal blood glucose and HbA1c) were significantly elevated in TC+DM group (all P<0.05), but showed no significant changes in TC group (all P>0.05). The proportions of large tumor diameter, lymph node metastasis, distant metastasis, and TI-RADS 4c and 5 nodules and multiple thyroid nodules in TC+DM group were significantly higher than those in TC group (all P<0.05); among patients with comorbid TC and DM, the proportions of distant metastasis and multiple nodules in high HbA1c group (HbA1c≥7%) were significantly higher than those in low HbA1c group (HbA1c<7%) (both P<0.05). In the 1 064 patients, 1 056 cases (99.2%) were papillary thyroid carcinoma (PTC), and all cases with comorbid TC and DM were PTC.
Conclusion: Comorbid TC and DM mostly occurs in older females, and this kind of patients have a higher TI-RADS classification, and are likely to develop multiple nodules, lymph node metastasis and distant metastasis. In patients with combined TC and DM, those with poor glucose control may have a high incidence of distant metastasis and multiple nodules. Therefore, older female DM patients with thyroid nodules should be vigilant to the occurrence of TC, and the nodules should be observed dynamically, along with tight blood sugar control.