Occurrence of Endocrine and Thyroid Cancers Among Alaska Native People, 1969-2013.

BACKGROUND: Nationwide, the incidence of thyroid cancer is lower among American Indian/Alaska Native (AI/AN) people than among U.S. whites (USW). However, little is known about the incidence of thyroid or other endocrine cancers specifically among Alaska Native (AN) people.

METHODS: Data were examined from the National Cancer Institute's Surveillance, Epidemiology, and End Results Alaska Native Tumor Registry on endocrine cancers diagnosed among AN people from 1969-2013, with a specific focus on thyroid cancers. Frequencies of endocrine cancers by site and also of thyroid cancers by histology, size, and stage at diagnosis were evaluated. Distributions were compared to USW (Surveillance, Epidemiology, and End Results 9 Registries) using the chi-square test. Five-year average annual age-adjusted incidence rates of thyroid cancers were calculated, stratified by histology, age, and five-year period of diagnosis, and compared to those observed among USW. Five-year cause-specific survival was evaluated using cause of death data from the National Death Index Plus from the National Center for Health Statistics.

RESULTS: During the 45-year period (1969-2013), 224 endocrine cancers were diagnosed among AN people, of which 210 (94%) were thyroid cancers. Compared to USW, AN people were diagnosed at a slightly younger age, had a higher proportion of thyroid cancers diagnosed with a size of 20-40 mm, and a larger proportion of patients with regional metastases. More than 85% of AN thyroid cancers were of papillary histology. The incidence of thyroid cancers was similar between AN people and USW, and appeared to increase among AN people over the period of surveillance. Finally, five-year cause-specific survival rate was 100% for papillary carcinoma patients and 86.3% [confidence interval 54.7-96.5] for follicular thyroid cancer patients.

CONCLUSIONS: This study is the first report of endocrine cancers and the first detailed examination of thyroid cancer among AN people. The incidence of thyroid cancer was similar among AN people and USW. However, compared to USW, AN people appear to be at risk for diagnosis at a younger age, larger size, and higher stage. Further research is needed to explore the causes of these differences.