The Bay Area Thyroid Cancer Study
Thyroid cancer is one of the most commonly occurring cancers among young women and in the rapidly growing population of Asian Americans. The higher incidence of thyroid cancer among Asian immigrants to the United States than among native Asian populations suggests that environmental (non-genetic) factors, such as nutrition, affect thyroid cancer risk.
Iodine is one nutrient that is essential in the synthesis of thyroid hormones and yet the research on the relationship between iodine exposure and thyroid cancer risk is limited and findings have been inconclusive. In this study we looked to quantify dietary iodine exposure in a diverse multicultural population, assess past exposure (i.e., one year ago) to iodine by obtaining toenail clippings and determine the association of iodine exposure to the most common type of thyroid cancer (papillary thyroid cancer). Upon completion of this study, it was concluded that there was, at most, a weak association between iodine exposure and the development of papillary thyroid cancer.
We also looked at the relationship between plant foods and the risk of thyroid cancer. We reported the first results on the relationship between phytoestrogens (found primarily in soy foods, whole grains, nuts and seeds, and some fruits and vegetables) and thyroid cancer risk, finding that greater consumption of these compounds was associated with a lower likelihood of developing this cancer. We also found that greater consumption of antioxidant vitamins (from foods such as oranges, broccoli, and carrots) and fiber (from foods such as beans and whole grains) reduced risk. Thus, a diet high in plant foods may help reduce a woman's likelihood of developing thyroid cancer.
We observed an increased risk of papillary thyroid cancer during the five years following a full-term pregnancy, supporting results from two previous studies suggesting that the thyroid may be particularly susceptible to damage during pregnancy and the early post-partum period.
Lastly, we examined why the rates of thyroid cancer are so high in women of southeast Asian heritage compared to US-born white women and women of northern Asian heritage. We found that the greater presence of goiter (thyroid enlargement) or thyroid nodules, strong risk factors for developing thyroid cancer, explained a substantial portion of the higher rates, with recent immigration being an important factor in Asian women of age 50 and older. Dietary patterns also contributed to the differences.
NCCC Principal Investigator: Pamela L. Horn-Ross, Ph.D.
Collaborators
NCCC: Dee W. West, Ph.D., Susan L. Stewart, Ph.D.
University of Missouri, Columbia: J. Steven Morris, Ph.D.
University of California, San Francisco: Marion Lee, Ph.D.
Stanford University: Alice S. Whittemore, Ph.D., I. Ross McDougall, M.B., Ch.B., Ph.D., Kent Nowels, M.D.
Funding: National Cancer Institute (R01 CA63284)
Publications:
Horn-Ross, PL, Morris, JS, Lee, M, West, DM, Whittemore, AS, McDougall, IR, Nowels, K, Stewart, SL, Spate, VL, Shiau, AC, Krone, MR. Iodine and thyroid cancer risk among women in a multiethnic population: the Bay Area thyroid cancer study. Cancer Epidemiology, Biomarkers and Prevention 10: 979-985, 2001.
Sakoda, LC and Horn-Ross, PL. Reproductive and menstrual history and papillary thyroid cancer risk: the San Francisco Bay Area thyroid cancer study. Cancer Epidemiology, Biomarkers and Prevention 11: 51-57, 2002.
Horn-Ross, PL, Hoggatt, KJ and Lee, MM. Phytoestrogens and thyroid cancer risk: the San Francisco Bay Area thyroid cancer study. Cancer Epidemiology, Biomarkers and Prevention 11: 43-49, 2002.
Haselkorn T, Stewart SL, Horn-Ross PL. Why are thyroid cancer rates so high in Southeast Asian women living in the United States? The Bay Area Thyroid Cancer Study. Cancer Epidemiology, Biomarkers and Prevention 12: 144-150, 2003.
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