Abstract: Background and purpose: The incidence of thyroid cancer (TC) is increasing worldwide. However, there were some differences among different regions. The purpose of this study was to investigate the incidence trends and clinicopathological characteristics of TC in Qingdao, a typical eastern coastal city, and to analyze the change in etiological spectrum of surgical thyroid diseases in recent years. Methods: A total of 2 251 patients who underwent thyroidectomy in 2014 due to thyroid nodules at the Affiliated Hospital of Qingdao University were retrospectively reviewed. The clinicopathological characteristics were further analyzed among 1 306 patients with TC and compared with the corresponding data from the Surveillance Epidemiology and End Results (SEER) database as well as previous data from this hospital. Results: With the increasing number of thyroidectomy in Qingdao, there was also an increase in the proportion of TC in patients after thyroidectomy, from 34.8% in 2010 to 59.0% in 2014. Among those with TC, the male-to-female ratio was 1∶2.80, with a relatively high incidence among 20-54 year-old adults, who were younger than those reported in terms of distribution of age in SEER database (U=2 289, P=0.000). About 50.2% of the TC patients were overweight or obese, 78.2% TC patients had only asymptomatic nodules detected by ultrasound at initial diagnosis, while 16.6% had visible or palpable thyroid nodules. Only 5.2% presented hoarseness or other repression symptoms. Micro-carcinoma accounted for 61.7% of TC in 2014 at this hospital, which was significantly higher than the proportion in 2010 (37.7%). Lymph node involvement was significantly more frequent at this hospital than in SEER database (49.5% vs 26.0%, χ²=11.806, P=0.001). Even among patients with micro-carcinoma, 31.3% already presented lymph node metastases. The proportions of papillary, follicular, medullary and anaplastic carcinoma were 97.5%, 1.1%, 1.0% and 0.5%, respectively, among which the percentage of papillary carcinoma was higher than that in SEER database (U=4 654.5, P=0.055). Conclusion: There was an increase in the number of thyroidectomy in Qingdao, and the preoperative diagnostic accuracy of TC in this area kept rising. The incidence of TC was relatively high in a younger population, with more common lymph node involvements and an overweight trend. The increasing proportion of micro-carcinoma might be related to the popularization of health examination. However, the frequent lymph node metastasis in patients with micro-carcinoma is an important indicator of the invasive behavior of micro-carcinoma, which should not be overlooked.

Key words: Thyroid cancer, Surgical therapy, Thyroid nodule, Clinicopathological characteristics