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Is soaring thyroid cancer rate due to overdiagnosis?

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Since 1975, the incidence of thyroid cancer has almost tripled in the United States. A new study published online on February 20 in the journal JAMA Otolaryngology has suggested that the increase may primarily due to overdiagnosis and treatment of tumors too small to ever cause harm. Previous research regarding other malignancies have questioned whether all cancers need aggressive treatment. These studies have suggested that, in addition to thyroid cancer, certain cancers of the prostate, breast, and lung grow so slowly that they will never become deadly; they note that overzealous screening leads to overtreatment.

The authors of the present study previously reported on a doubling of thyroid cancer incidence, which was primarily due to the detection of small papillary thyroid cancers. Papillary cancers are the most common type of thyroid cancer; they are often discovered during an autopsy in people who have died of other causes. The investigators argue that, inasmuch as thyroid cancer deaths has remained stable while the diagnostic rate has soared, the increased incidence is due to overdiagnosis. Therefore, the investigators conducted a study to determine whether thyroid cancer incidence has stabilized.

The researchers conducted an analysis of trends in patients diagnosed with thyroid cancer from 1975 through 2009; they accessed data from the Surveillance, Epidemiology, and End Results (SEER) program and thyroid cancer mortality from the National Vital Statistics System. Nine SEER locations (SEER 9) were evaluated: Atlanta, Georgia; Connecticut; Detroit, Michigan; Hawaii; Iowa; New Mexico; San Francisco–Oakland, California; Seattle–Puget Sound, Washington; and Utah. Included in the study were men and women older than 18 years who were diagnosed with thyroid cancer between 1975 and 2009 who resided in one of the SEER 9 areas. The main outcome measures were: the incidence of thyroid cancer; type of cancer determined by microscopic diagnosis; tumor size; and patient mortality.

The study authors found that since 1975, the incidence of thyroid cancer almost tripled, from 4.9 to 14.3 per 100,000 individuals (absolute increase: 9.4 per 100,000). All of the increase was attributable to papillary thyroid cancer; the incidence increased from 3.4 per 100,000 to 12.5 per 100,000. The absolute increase in thyroid cancer in women was almost four times higher than that of men. In addition, from 1975 through 2009, the mortality rate from thyroid cancer was stable (approximately 0.5 deaths per 100,000).

The authors concluded that an ongoing epidemic of thyroid cancer is underway in the US. However, they note that the epidemiology of the increased incidence suggests that it is not an epidemic of disease but rather an epidemic of diagnosis. They explain that the problem is particularly severe for women, who have lower autopsy prevalence of thyroid cancer than men but higher cancer detection rates by a 3:1 ratio.

The researchers are affiliated with the Department of Veterans Affairs Medical Center (White River Junction, Vermont), Section of Otolaryngology, Geisel School of Medicine, Dartmouth College (Hanover, New Hampshire), and Dartmouth Institute for Health Policy and Clinical Practice (Hanover, New Hampshire).

The first sign of thyroid cancer is usually a painless lump in the neck. Other symptoms may include:

  • Hoarseness or loss of voice as the cancer presses on the nerves to the voice box
  • Difficulty swallowing as the cancer presses on the throat
  • Throat or neck pain that does not go away
  • Breathing problems
  • A cough that does not go away

Take home message:
Thyroid cancer treatment often includes surgery to remove the gland. Most surgeries contain risks and consequences. Following the surgery, the patient must take thyroid medication for the rest of his or her life. The thyroid gland also contains parathyroid glands, which are responsible for controlling the body’s calcium levels. If these glands are damage during the surgery, a condition known as hypoparathyroidism. This condition results in lowered calcium levels, which can cause problems ranging from mild to life threatening.