Background: An increasing incidence of thyroid cancer is observed in many developed countries. Increasing incidence may also reflect better reporting or increased diagnostic scrutiny. We conducted this study to examine trends in thyroid cancer incidence and histological patterns in Sri Lanka.
Methods: A retrospective cohort evaluation of patients with thyroid cancer during 2001-2010 was performed using population based data published from the Sri Lanka National Cancer Registry. Trends in incidence and histological patterns were analysed by age and gender.
Results: The age-standardized incidence of thyroid cancer increased from 2.44 per 100,000 in 2001 (95% confidence interval [95% CI]: 2.21-2.67) to 5.16 per 100,000 in 2010 (95% CI: 4.85-5.47); a 2.1-fold increase (p < 0.05 for trend). A greater part of this increase is attributable to increase in incidence of papillary thyroid cancer, which increased from 1.64 to 3.61 per 100,000; a 2.2-fold increase (p < 0.05 for trend). Follicular cancer showed lesser, yet a significant increase from 0.56 to 0.95 per 100,000 (p < 0.05). Other varieties of thyroid cancer showed no significant increases in incidence. Trends in the increases in incidence of papillary cancer in females showed a much greater increase compared with males (from 2.45 to 5.60 per 100,000, a 2.28-fold increase in females compared with from 0.82 to 1.55; a 1.89-fold increase in males, p < 0.001). Highest incidence of papillary cancer was observed in 30-39-year age group, which has increased from 5.56 to 12.9 per 100,000; a 2.32-fold increase (p < 0.001).
Conclusions: The increasing incidence of thyroid cancer in Sri Lanka is predominantly due to the increasing incidence of papillary cancers. These trends may reflect increased detection and better reporting, although an inherent increase in the incidence is the likely main contributor. Further studies including tumour stage and mortality may help answer these questions.
Keywords: Incidence; Papillary cancer; Thyroid cancer.