The dramatic rise in the reported cases of thyroid cancer in the U.S., which tripled since the 1970s, can be attributed not to actual cancer but to overdiagnosis.

A new study, led by Dr. Louise Davies and Dr. H. Gilbert Welch, has analyzed mortality records from the National Vital Statistics System between 1975 and 2009 and diagnostic trends from the population-based Surveillance, Epidemiology, and End Results (SEER) 9 program. The records studied covered the cities of Atlanta, Connecticut, Detroit, the San Francisco-Oakland area, and the Seattle-Puget Sound area, as well as the states of Hawaii, Iowa, New Mexico, and Utah. The data studied were of those aged 18 years and older and diagnosed with thyroid cancer between 1975 and 2009 in these areas.

The findings, published in JAMA Otolaryngology - Head and Neck Surgery, has revealed that the reported number of cases of thyroid cancer rose from 4.9 to 14.2 for every 100,000 people. The increase was greater in women than in men, although the death rate for thyroid cancer for the period covering 1975 through 2009 remained stable at 0.5 deaths per 100,000 individuals.

The study has also found that the increase of incidence in thyroid cancer diagnoses can be attributed to the detection of small papillary cancer, which is a less aggressive form of cancer, and not likely to cause death or disease. For the researchers, this translates to an epidemic of over-diagnosis, which in turn raises the question of whether all cancers, regardless of gravity, required aggressive treatment.

The thyroid is a butterfly-shaped gland located at the front of the neck, and creates the hormones that help regulate how the body uses energy. Thyroid cancer happens when abnormal cells begin to grow in the thyroid gland, which impedes the proper function of the thyroid. Treatment for thyroid cancer often involves removal of the gland, followed by a lifelong daily maintenance with hormone medication. For lower-risk thyroid tumor, less aggressive treatment is needed, but data shows that thyroid removal is done on 85 percent of all patients diagnosed with the cancer.

With the dramatic rise of incidence in thyroid cancer that the study found, the researchers say that patients are not only over-diagnosed, but also they are undergoing treatment and surgery that may not be necessary.

"Our old strategy of looking as hard as possible to find cancer has some real side effects," said Dr. Gilbert Welch, co-author of the thyroid study and a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice.

"There is an ongoing epidemic of thyroid cancer in the United States. The epidemiology of the increased incidence, however, suggests that it is not an epidemic of disease but rather an epidemic of diagnosis," the researchers concluded.