Sharp Rise in Thyroid Cancer Linked to Modifiable Behavioral or Environmental Factors, CPIC Study Finds

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Thyroid cancer increased from 14th to 5th most common cancer in women over last 20 years

We found significant increases in thyroid cancer rates for men and women of all population groups and for all sizes and stages of tumors.

The dramatic increase in the incidence of thyroid cancer worldwide over the past three decades likely relates to modifiable behavioral or environmental factors, as opposed to improved diagnostic capability, according to researchers at the Cancer Prevention Institute of California (CPIC) and their colleague at the Stanford University School of Medicine.

“Thyroid cancer is increasing at an alarming rate in the population as a whole,” said CPIC Senior Scientist Pamela Horn-Ross, Ph.D., lead author of the study. “The significant, rapid and continual increase of this cancer throughout the diverse population of California over the last 20 years deserves our attention.”

Thyroid cancer is now the fifth most common cancer in women, up from 14th most common 20 years ago. The rate of this cancer in women doubled between 1990 and 2005. It increased by 66 percent in men during this time period.

The researchers conducted a broad study examining 22 years of incidence data across patients of all ages, ethnicities and socio-economic levels.

“We found significant increases in thyroid cancer rates for men and women of all population groups and for all sizes and stages of tumors,” Dr. Horn-Ross said. “While improvements in diagnostic technology most likely account for some portion of this increase, our analysis points squarely to a role for non-genetic factors in our behavior or environment as significantly impacting the continued rise in thyroid cancer rates.”

“The factor or factors are unknown but are probably modifiable,” said CPIC Scientist Christina A. Clarke, Ph.D., who co-authored the study. “Armed with a better understanding of how rapidly changing environment or behavior impact the development of thyroid cancer, appropriate changes could be made to mitigate that risk.”

The researchers conducted a comprehensive evaluation of factors including patient age, sex, race/ethnicity, birthplace; tumor size and stage at time of diagnosis; socio-economic status; and residence in an ethnic enclave. An ethnic enclave is defined as a neighborhood that is ethnically and culturally distinct from the surrounding region, with greater co-ethnic social support and maintenance of native diets and lifestyles. The inclusion of trends by birthplace and ethnic enclave expands upon previous studies where this information was not available.

Among the various types of thyroid cancer, papillary is by far the most common, accounting for more than 80 percent of the cases diagnosed in both men and women. The incidence of papillary thyroid cancer has increased significantly in both genders between 1988 and 2009, (the last year for which data was available at the time the study was conducted), with an accelerated increase in women after 2001. Women also experienced an increase in follicular thyroid cancer, but not other types of thyroid cancer, the researchers noted.

The study, “Continued rapid increase in thyroid cancer incidence in California: trends by patient, tumor and neighborhood characteristics,” was published online today in the journal Cancer Epidemiology, Biomarkers & Prevention (CEBP). In addition to Drs. Horn-Ross and Clarke, the study was authored by CPIC researchers Daphne Y. Lichtensztajn, M.D., Ingrid Oakley-Girvan, Ph.D., Peggy Reynolds, Ph.D., Scarlett Lin Gomez, Ph.D., and David O. Nelson, Ph.D.; and Chrysoula Dosiou, M.D. of the Division of Endocrinology at the Stanford University School of Medicine.

About the Cancer Prevention Institute of California
The Cancer Prevention Institute of California (CPIC) is the nation’s premier organization dedicated to preventing cancer and to reducing its burden where it cannot yet be prevented. CPIC tracks patterns of cancer throughout the entire population and identifies those at risk for developing cancer. Its research scientists are leaders in investigating the causes of cancer in large populations to advance the development of prevention-focused interventions. CPIC’s innovative cancer prevention research and education programs, together with the work of the Stanford Cancer Institute, deliver a comprehensive arsenal for defeating cancer. For more information, visit CPIC’s official website at

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