According to a new study published in JAMA Otolaryngology-Head & Neck Surgery, increased incidence of thyroid cancer may not be because of an increase in the disease, but an increase in diagnosis.

Several types of cancer can affect the thyroid – a gland in the neck that produces hormones. Factors that make people more at risk of getting thyroid cancer include:

  • Being between the ages of 25 and 65
  • Being female
  • Being Asian
  • Having a history of thyroid disease in the family
  • Having previously had radiation treatments to the head or neck.

To diagnose thyroid cancer, doctors use a combination of physical exam, blood tests, imaging tests and a biopsy.

Since 1975, the incidence of thyroid cancer has nearly tripled, from 4.9 to 14.3 in every 100,000 people.

To assess why there has been an increase in diagnoses of thyroid cancer, the authors behind the new study analyzed the medical records of patients between 1975 and 2009 in Atlanta, GA; Connecticut; Detroit, MI; Hawaii; Iowa; New Mexico; Utah; the San Francisco-Oakland area in California and the Seattle-Puget Sound area of Washington.

Despite the increase in diagnosis, the researchers did not find an increase in the rates of death from thyroid cancer. About 0.5 per 100,000 people die from this cancer, which has remained stable since 1975.

Because of this, the researchers suspected that “overdiagnosis” may be responsible for rise in thyroid cancer incidence. Overdiagnosis is when a patient is diagnosed with having a condition that has no symptoms and may never cause them any harm.

The researchers found that increased detection of small papillary cancers – a less aggressive form of thyroid cancer – is responsible for the increase in thyroid cancer incidence.

As a response to this overdiagnosis, the researchers make several suggestions. They think that some of the small papillary cancers may benefit from not being labeled as cancer, and instead of treating the small papillary cancers, monitoring them through active surveillance instead.

Doctors should explain to patients that many of these small cancers will never grow or cause them any harm, the researchers say. The researchers do concede, though, that it is not possible to know in advance which of these diagnosed cancers will continue to be small and not cause symptoms and which will grow to be a threat to the patient’s health.

The study also recommends that the risk factors for thyroid cancer need to be more closely investigated.

The authors conclude:

We found that there is an ongoing epidemic of thyroid cancer in the United States. It does not seem to be an epidemic of disease, however. Instead, it seems to be substantially an epidemic of diagnosis: thyroid cancer incidence has nearly tripled since 1975, while its mortality has remained stable.”

In 2013, Medical News Today reported on a study finding that recurrence of papillary thyroid cancer following surgery could be predicted by measuring sections of genetic material within the tumors.