Why the Rising Incidence of Thyroid Cancer?
An estimated 56,460 new cases of thyroid cancer are expected to be diagnosed in 2012 in the US, with 75 percent of cases occurring in women, according to the American Cancer Society (ACS). The incidence rate of thyroid cancer has more than doubled since 1990, and, according to the ACS, "it is the fastest-increasing cancer in both men and women. Since 2004, incidence rates have been increasing by 5.5 percent per year in men and 6.6 percent per year in women."
The rise in deaths attributable to thyroid cancer, however, has been less dramatic: From 2004 to 2008, the death rate for thyroid cancer increased slightly from 0.47 (per 100,000) to 0.50 in men, and from 0.47 to 0.52 in women. ACS projects an estimated 1,780 deaths from thyroid cancer in the US in 2012.
Nevertheless, the sharp increase in incidence has led to much debate within the scientific community. To a large extent, the increase is attributable to improved diagnosis. Over the last 30 years, notes the Northwestern University Institute for Women's Health Research Blog, "ultrasound and fine-needle biopsies have helped diagnose cases that would never have been found before."
The blog cites findings of a study published in the Journal of the American Medical Association in 2006 that concluded that the 140 percent increase in thyroid cancer from 1973 to 2002 was a result of "increased diagnostic capacity." The authors maintained that most of the tumors detected were "extremely small, papillary thyroid cancer tumors... that would have never caused problems in the majority of cases." The blog concedes, however, that other "unknown factors" also play a role.
A study published in the journal Environmental Health Perspectives in 2010 found that people with high levels of the chemical perfluorooctanoic acid (PFOA) in their blood were twice as likely to have thyroid problems as those with the lowest levels. Data was obtained from medical records of nearly 4,000 otherwise healthy US adults. Studies in animals have found that PFOA and a related substance, perfluorooctane sulfonate (PFOS), can cause thyroid problems as well as hormone imbalances, liver disease, and cancer.
The substance is so stable that it persists for years. Trace levels of PFOA have been detected in people around the world and in wildlife as diverse as birds, fish, and polar bears. "It's been thought that because they're inert they don't cause any health problems, but we're starting to see some evidence that is suggesting that's not true," said Tamara Galloway, professor of ecotoxicology at Exeter University, one of the authors of the study.
"Because these chemicals are inert they are persistent and they build up in the environment and also in human and animal tissues." High levels of PFOA have been found in drinking water in US communities contaminated by fluoropolymer production facilities in Ohio and West Virginia.
PFOA is a man-made chemical known for its heat resistance and water-, grease-, and stain-repelling properties. Manufacturers use PFOA to make fluoropolymers, used in non-stick coatings for cookware, flame retardants in furnishings, stain protection treatments for carpets, wire coatings, and waterproof clothing such as Gore-Tex. The US Food and Drug Administration has a voluntary agreement with several companies to phase out PFOA production over the next few years.
The good news, according to the ACS, is that regardless of cause, the five-year relative survival rate for all thyroid cancer patients is 97 percent. Survival varies, however, by stage, age at diagnosis, and disease subtype. Thus, the five-year survival rate approaches 100 percent for localized disease, is 97 percent for regional-stage disease, and stands at only 56 percent for distant-stage disease. For all stages combined, survival is highest for patients under 45 years old (almost 100 percent), progressively decreasing to 82 percent for those 75 or older.
The rise in deaths attributable to thyroid cancer, however, has been less dramatic: From 2004 to 2008, the death rate for thyroid cancer increased slightly from 0.47 (per 100,000) to 0.50 in men, and from 0.47 to 0.52 in women. ACS projects an estimated 1,780 deaths from thyroid cancer in the US in 2012.
Nevertheless, the sharp increase in incidence has led to much debate within the scientific community. To a large extent, the increase is attributable to improved diagnosis. Over the last 30 years, notes the Northwestern University Institute for Women's Health Research Blog, "ultrasound and fine-needle biopsies have helped diagnose cases that would never have been found before."
The blog cites findings of a study published in the Journal of the American Medical Association in 2006 that concluded that the 140 percent increase in thyroid cancer from 1973 to 2002 was a result of "increased diagnostic capacity." The authors maintained that most of the tumors detected were "extremely small, papillary thyroid cancer tumors... that would have never caused problems in the majority of cases." The blog concedes, however, that other "unknown factors" also play a role.
A study published in the journal Environmental Health Perspectives in 2010 found that people with high levels of the chemical perfluorooctanoic acid (PFOA) in their blood were twice as likely to have thyroid problems as those with the lowest levels. Data was obtained from medical records of nearly 4,000 otherwise healthy US adults. Studies in animals have found that PFOA and a related substance, perfluorooctane sulfonate (PFOS), can cause thyroid problems as well as hormone imbalances, liver disease, and cancer.
The substance is so stable that it persists for years. Trace levels of PFOA have been detected in people around the world and in wildlife as diverse as birds, fish, and polar bears. "It's been thought that because they're inert they don't cause any health problems, but we're starting to see some evidence that is suggesting that's not true," said Tamara Galloway, professor of ecotoxicology at Exeter University, one of the authors of the study.
"Because these chemicals are inert they are persistent and they build up in the environment and also in human and animal tissues." High levels of PFOA have been found in drinking water in US communities contaminated by fluoropolymer production facilities in Ohio and West Virginia.
PFOA is a man-made chemical known for its heat resistance and water-, grease-, and stain-repelling properties. Manufacturers use PFOA to make fluoropolymers, used in non-stick coatings for cookware, flame retardants in furnishings, stain protection treatments for carpets, wire coatings, and waterproof clothing such as Gore-Tex. The US Food and Drug Administration has a voluntary agreement with several companies to phase out PFOA production over the next few years.
The good news, according to the ACS, is that regardless of cause, the five-year relative survival rate for all thyroid cancer patients is 97 percent. Survival varies, however, by stage, age at diagnosis, and disease subtype. Thus, the five-year survival rate approaches 100 percent for localized disease, is 97 percent for regional-stage disease, and stands at only 56 percent for distant-stage disease. For all stages combined, survival is highest for patients under 45 years old (almost 100 percent), progressively decreasing to 82 percent for those 75 or older.
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