As overall cancer rates decline in the U.S., thyroid cancer counters the trend

As overall cancer rates are declining in the United States, thyroid cancer counters the trend. It's being diagnosed more frequently, especially in women. Women are three times more likely than men to develop thyroid cancer.

The April issue of Mayo Clinic Women's HealthSource provides an overview of thyroid cancer, what may be behind some of the increasing numbers, and warning signs of the disease.

The thyroid is the butterfly-shaped gland at the base of the neck, just below the Adam's apple. It produces two hormones that help regulate the heart rate, blood pressure, body temperature and weight.

Cancer occurs when the cells in the thyroid gland change and grow in an uncontrolled fashion, forming a malignant nodule or tumor. Thyroid nodules are common with aging and more than 90 percent are noncancerous. Still, doctors often recommend evaluating nodules to confirm if they are cancerous or benign.

The exact cause of thyroid cancer isn't known. Research has shown that radiation exposure, family history, increasing age and having too much or too little iodine in the diet could increase the risk of this uncommon disease. It's estimated that more than 37,000 people in the United States will be diagnosed with thyroid cancer this year.

Some research indicates that the jump in thyroid cancer diagnoses is due to the increasing use of imaging tests, such as ultrasound, which are spotting small tumors that may not have been found in the past. However, studies have found that both large and small thyroid tumors are now being found more often, suggesting that advanced imaging technology isn't the only factor contributing to the increasing number of thyroid cancer cases.

Early on, thyroid cancer doesn't cause symptoms. As the cancer grows, symptoms might include:

- A neck lump that can be seen or felt

- Persistent hoarseness, or difficulty speaking in a normal voice

- Enlarged lymph nodes, especially in the neck

- Difficulty swallowing or breathing

- Pain in the throat or neck

While these symptoms can be caused by conditions other than thyroid cancer, they should be pointed out to a physician.

Thyroid cancer, for the most part, is considered one of the least deadly cancers. Surgery to remove all or part of the thyroid is the most common treatment. The death rate has remained low for the most common forms of thyroid cancer even as the number of patients diagnosed climbs.