LIFESTYLE ETIOLOGY OF THYROID CANCER IN A MULTIETHNIC POPULATION

Abstract

Thyroid cancer is ranked 9th cancer in the world, 12th in the United States and in the top 10 for Hawaii. It is the most common endocrine cancer and the most common in persons under 40 years old, with an over 98% 5-year survival. Globally the age standardized incidence rates have been going up in the last 30 years in all age groups and in both sexes. Hawaii has high rates of thyroid cancer, with only 1 case control study that was conducted in Hawaii. There are sex and racial/ethnic disparities; with a 3:1 ratio: women compared to men having higher incidence than men, and Filipinos having higher incidence rates compared to other racial/ethnic groups. This research will add to the existing gap in the body of literature on diverse disaggregated racial/ethnic groups. The disparities, rising trends, and financial, emotional, and physical burdens makes this research of public health importance. This dissertation uses the Multiethnic Cohort Study which is a prospective cohort study that has high risk racial/ethnic groups: such as Filipinos, and a wide range of exposures. The only established risk factor is radiation, although there are probable lifestyle risk factors in the literature. Study 1 examined the association of lifestyle risk factors by sex and race/ethnicity. In study 1 there was a statistically significant increased risk of adiposity and diabetes, and suspected increased risk among high neighborhood socioeconomic status and farming occupation, with a protective effect for smoking pack years and alcohol consumption. Some of these associations were statistically significant in some racial/ethnic groups, but heterogeneity was not significant. Reproductive factors in women have been hypothesized as contributors for higher incidence rates compared to men, as rates peak around menopausal age, 40-49, in women contrary to men at 60-69; thus study 2 examined the association of reproductive factors and thyroid cancer in women by race/ethnicity. There was a statistically significant increased risk of thyroid cancer for women having a surgical menopause, oophorectomy, hysterectomy, and nulliparity; with suggestive increased risk for former users of MHT, and women with a history of induced abortion and stillbirth. In final study of survival among thyroid cancer cases, overall, 5-year survival was over 70%. All-cause mortality was higher in men compared to women and with disparities observed among AA, NH and Filipinos compared to JA that mirror mortality in the general population. When TC cases were compared to matched controls with no TC in the MEC, men and Filipino TC cases exhibited an excess mortality due to TC.