Ten-year Thyroid Cancer Incidence in an Integrated Healthcare Delivery System.

Introduction: The incidence of papillary thyroid cancer (PTC) has increased in recent decades, but data from community-based settings are limited. This study characterizes PTC trends in a large, integrated healthcare system over 10 years.

Methods: The annual incidence of PTC (2006-2015) was examined among Kaiser Permanente Northern California adults aged 21 to 84 years using Cancer Registry data, including tumor size and stage. Incidence estimates were age-adjusted using the 2010 US Census.

Results: Of 2990 individuals newly diagnosed with PTC (76.8% female, 52.7% non-Hispanic White), 38.5% and 61.5% were aged < 45 and < 55 years, respectively. At diagnosis, 60.9% had PTC tumors ≤ 2 cm, 9.2% had tumors > 4 cm, and 66.1% had Stage I disease. The annual age-adjusted incidence of PTC increased from 9.4 (95% confidence interval [CI] = 8.1-10.7) to 14.5 (95% CI = 13.1-16.0) per 100,000 person-years and was higher for female patients than for male patients. Incidence tended to be higher in Asian/Pacific Islanders and lower in Black individuals. Increasing incidence was notable for Stage I disease (especially 2006-2012) and evident across a range of tumor sizes (3.0-4.6 for ≤ 1 cm, 2.5-3.5 for 1-2 cm, and 2.4-4.7 for 2-4 cm) but was modest for large tumors (0.9-1.5 for > 4 cm) per 100,000 person-years.

Discussion: Increasing PTC incidence over 10 years was most evident for tumors ≤ 4 cm and Stage I disease. Although these findings may be attributable to greater PTC detection, the increase across a range of tumor sizes suggests that PTC burden might also have increased.