Rising thyroid cancer incidence in Kerala: Is it real or over diagnosis?

Abstract

e17589 Background: There has been an increase in the incidence of thyroid cancer in India and in high income countries. One of the reasons for this has been attributed to the large number of screening programs. Kerala state ranks second highest in the incidence of thyroid cancer in India. Screening provides the advantage of early detection of cancer and successful treatment but also tends to over diagnose. Methods: To study the trend of incidence of primary thyroid cancer among newly diagnosed cancer patients and its association with the mode of detection, we retrospectively reviewed hospital based cancer registry data of patients with thyroid cancer who were treated at AIMS (Amrita Institute of Medical Sciences), Kochi between 2004-2014. All patients who were newly diagnosed with primary thyroid cancer at our center or referred to us after initial surgery were included in this analysis. Patients with recurrent cancer/metastases were excluded. Results: We analyzed the records of 2,315 newly diagnosed thyroid cancer patients. Median age was 44.1yrs (range 13-90yrs). There were 619 males and 1696 females. Papillary type was the most common 85.8% followed by follicular type 7.4%. 1235 cases were operated at AIMS. 74 cases (3.2%) were diagnosed incidentally by Ultrasonography/PET scan/CT scan. All others (97% n = 2,245) presented with neck swelling. It was seen that the proportion of new cases of thyroid cancer among all new cancer cases was increasing serially from 4.6 % (n = 106, 95% 2004) to 7.4% (n = 195) to13.7% (n = 317, 2014). There was a significant increase in the number of cases of T1a and T1b at the time of diagnosis during the study period (n = 1235, p value < 0.001 and p value for trend < 0.001 respectively) which indicates that there was early diagnosis. 97% of the cases presented with thyroid related symptoms indicating that clinical presentation has still been the main mode of detection in our series. Conclusions: Our data shows that there may be a true increase in the number of cases of thyroid cancer as majority presented with clinical symptoms, except few detected incidentally. As it is a single institution based data we need further studies to see if over use of USG based imaging for any thyroid swelling is responsible for an apparent increase in the number of thyroid cancer cases.