Thyroid Cancer Is Rising But Who Knows Why?

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Investigators have noted that thyroid cancer is rising dramatically around the world and has been for more than 30 years. Several questions immediately come to mind when hearing this statement, and the research team at the Cancer Prevention Institute of California (CPIC) and Stanford University School of Medicine provide some answers, albeit not necessarily satisfying ones.

Who was studied?
Under the direction of Pamela Horn-Ross, PhD, a senior scientist at CPIC, the team evaluated data spanning 22 years. Patient information came from individuals of all ages, socioeconomic levels, and ethnicities. The analysis yielded some startling results:

  • Among women, thyroid cancer ranks as the fifth most common cancer, a dramatic shift from the 14th position two decades ago
  • Between 1990 and 2005, the rate of thyroid cancer doubled in women and increased by 66 percent in men
  • More than 80 percent of thyroid cancer cases diagnosed in men and women are papillary, which also increased significantly in both sexes
  • An increase in the incidence of follicular thyroid cancer was seen in women (there are four types of thyroid cancer: follicular, papillar, medullary, and anaplastic)

Now comes the inevitable question.

Why is thyroid cancer incidence rising?
I asked that question directly to Christina A. Clarke, PhD, another CPIC scientist who co-authored the study, and offered several potential culprits. She explained in her correspondence that “We suspect the factors are modifiable given the trends that we have seen in incidence in recent years (these trends would rule out genetics or simply better surveillance), but we really don’t know what they are.”

Therefore, improved screening and diagnostic methods as well as genes are not part of the rising trend in thyroid cancer. Could some of those mystery factors involve food choices, pesticide use, radiation exposure, and other environmental issues?

Other studies provide clues
Thyroid cancer is on the minds of many researchers, as evidenced by the numerous new studies on the topic. A few of them offer some clues as to why the incidence of this cancer is rising.

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A new study appearing in the British Journal of Medicine reported that eating red meat, sodium, and obesity were all associated with an increased incidence of cancer overall among men and both gastric and thyroid cancers in particular in a population of more than 8,000 Korean adults. The study focused on diet and noted that Koreans have been rapidly adopting the Western diet over their traditional Korean diet.

Another recent study investigated risk factors for thyroid cancer among natives of French Polynesia, an area of the world that has an unusually high incidence of this cancer. The identified risk factors included thyroid radiation dose received from nuclear fallout in individuals before age 15 obesity, artificial menopause, family history of thyroid cancer, low intake of dietary iodine, personal history or head and/or neck irradiation, having a large number of children, and drinking water from a spring.

The authors concluded that except for smoking, the risk factors for thyroid cancer among this specific population were similar to those in other societies around the world. The role of drinking water could be associated with geological elements.

Occupation also may play a part in your risk for thyroid cancer. Data from 30 studies were analyzed by a team at the University of Chicago. They found consistent relationship between healthcare occupations and radiation-exposed individuals and thyroid cancer risk. Inconsistent associations were seen in people who worked with pesticides and the agricultural industry.

Yet one more new study supported the relationship between obesity and the risk of thyroid cancer, specifically papillary. An analysis of data from three studies involving more than 1,900 patients with thyroid cancer and more than 2,100 cancer-free controls showed a significant increased risk of thyroid cancer in obese women and men when compared with normal weight adults.

Apparently there is a lot of interest in uncovering the mysteries of thyroid cancer, including identification of its risk factors. So far no one is certain why thyroid cancer is rising, but the increase in research may hopefully turn up some answers soon and allow people to make changes that can alter the incidence of the disease.

SOURCES
Aschebrooke-Kilfoy B et al. Occupation and thyroid cancer. Occupational and Environmental Medicine 2014 May; 71(5): 366-80
Horn-Ross PL et al. Continued rapid increase in thyroid cancer incidence in California: trends by patient, tumor, and neighborhood characteristics. Cancer Epidemiology, Biomarkers and Prevention 2014 May 19 pub. Online
Wie GA et al. Red meat consumption is associated with an increased overall cancer risk: a prospective cohort study in Korea. British Journal of Nutrition 2014 Apr 28:1-10
Xhaard C et al. Differentiated thyroid carcinoma risk factors in French Polynesia. Asian Pacific Journal of Cancer Prevention 2014; 15(6): 2675-80
Xu L et al. Obesity and the risk of papillary thyroid cancer: a pooled analysis of three case-control studies. Thyroid 2014 May 5

Image: Wikimedia Commons

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Comments

Excellent coverage of this. I have wondered about radiation in the environment - and medical imaging to be honest.
Thank you. I hope research into this question will continue and provide actionable answers.
One of the most common radioactive elements released from nuclear facilities of any type is radioactive iodine, which, of course, accumulates in the thyroid. In the past the US government deliberately released radioactive iodine among US populations to track it and calculate how damaging it might be. I wonder what total tonnage of iodine is being emitted from the varied nuclear facilities we maintain.