Thyroid cancer incidence and trends by demographic and tumor characteristics in Oran, Algeria: 1993-2013, a population-based analysis

Objectives Incidence rates of thyroid cancer have dramatically increased over recent decades in many countries, particularly the papillary histotype and microcarcinomas. We examined thyroid cancer incidence and trends by demographic and tumor characteristics based on 1443 patients with thyroid cancer diagnosed between 1993 and 2013 in Oran district, in Northwest Algeria. Methods All thyroid cancer cases were abstracted from medical records and pathology reports and classified according to the International Classification for Diseases in Oncology, third edition. Age-specific, age-standardized incidence rates per 100 000 person-years, and annual percent changes (APC) in the incidence were calculated. Results Age-standardized incidence was 11.7 per 100 000 for women and 2.0 per 100 000 for men. Thyroid cancer incidence increased over time significantly in women (APC: +3.72%; P < 0.05), mostly due to an increased incidence of the papillary histotype (APC: +5.48%; P < 0.05), and microcarcinomas (APC: +17.34%; P < 0.05). During the same time period, the incidence of follicular thyroid carcinomas decreased (APC: -3.74%; P < 0.05). Conclusions The results of our study showing an upward trend of thyroid cancer incidence driven largely by increases in the papillary histotype are consistent with previous studies. The higher increase has coincided with the introduction of fine needle aspiration and thyroid ultrasound in the 1990s, and may have led to overdiagnosis. However, the increased papillary-to-follicular ratio observed over time is possibly a late effect of iodine supplementation implemented in Algeria in 1967 to combat endemic goiter. Further larger-scale population-based research is needed to gain insight into thyroid cancer etiology.