More and more Americans are getting thyroid cancer. The incidence of new cases has doubled in the last 40 years, making it the fastest-increasing cancer in the US. In the years between 1997 and 2006, the incidence of thyroid cancer increased by 6.5% per year, according to data from the National Cancer Institute.
Here, who gets thyroid cancer and why it’s on the rise…
You can feel the outline of the thyroid gland by touching the area on the neck just below the Adam’s apple. It’s an endocrine (hormone-producing) gland that secretes triiodothyronine (T3) and thyroxine (T4), hormones that regulate metabolism, heart rate and many other functions.
The most common type of thyroid cancer, papillary thyroid cancer, accounts for about 80% of all cases. It usually is diagnosed when patients are in their mid-40s, and women get it about three times more often than men.
In the majority of cases of thyroid cancer, there are no obvious causes. However, there are some exposures and conditions that have been identified as risk factors…
Radiation exposure. Exposure to high levels of radiation from fallout from nuclear power plant accidents and weapons testing has been linked to thyroid cancer.
Also at risk are adults who were treated with radiation during childhood for chronic conditions, such as acne and enlarged tonsils and adenoids. Radiation was used excessively from the 1940s through the 1960s for benign conditions of the head and neck before the risks were fully understood.
Important: Routine exposures during regular X-rays and CT scans at the dentist’s or doctor’s office have not been shown to result in higher rates of thyroid cancer. In addition, higher treatment doses, such as external beam radiation used to treat head and neck cancer, also have not resulted in increased risk.
Hashimoto’s thyroiditis is an autoimmune disease that affects the thyroid gland. It greatly increases the risk for thyroid lymphoma, a less common form of thyroid cancer. Patients with Hashimoto’s thyroiditis also have a significantly greater risk of getting papillary thyroid cancer. So if you have Hashimoto’s thyroiditis, you should see your doctor regularly to be monitored for thyroid deficiency.
Goiter. This is an enlarged thyroid gland, commonly caused by low dietary iodine or other environmental factors.
Being overweight increases the risk for thyroid cancer by about 20%. Patients who are obese are even more likely to get it.
Genetics. While the majority of thyroid cancers do not run in families, there are specific genetic syndromes, including multiple endocrine neoplasia, that increase the risk for thyroid cancer. If you have a strong family history of thyroid cancer, you should ask your doctor if further testing is desirable.
Keep in mind that the total number of thyroid cancer cases is relatively low. It is estimated that there will be about 60,220 new cases in 2013. (For comparison, about 234,580 new cases of breast cancer and 142,820 new cases of colorectal cancer will be diagnosed this year.)
Specialists who treat thyroid cancer agree that they’re seeing more cases in recent years. But what they don’t know is exactly why.
In addition to the risk factors listed above, it’s possible that environmental factors, such as exposure to chemical pollutants, are involved. No definitive study, however, has confirmed environmental agents are responsible.
Also, because women and obese individuals have higher levels of estrogen, it has been suggested that estrogen may be an additional risk factor.
Another factor: Improvements in diagnosis. With the development of ultrasound in the 1980s, it’s now possible to detect thyroid nodules that are smaller than one centimeter (cm) across.
A study in The Journal of the American Medical Association found that much of the increase in reported cases of thyroid cancer was due to small tumors that might never have been discovered in the past. Many of these tumors are unlikely to grow large enough to cause symptoms.
A typical symptom of thyroid cancer is a painless lump in the gland. Advanced cases may result in enlarged lymph nodes, changes in the voice (hoarseness), difficulty swallowing or breathing, or even coughing up blood.
Most thyroid nodules are discovered by palpation—doctors feel them when they check the neck during routine exams. Or an abnormality might be discovered when you have an ultrasound or other imaging test for an unrelated condition, such as neck pain after a car accident.
If a nodule is detected, you will be scheduled for blood tests (to check levels of thyroid hormones) and an ultrasound. Then if the nodule still seems suspicious, your doctor may order a fine-needle biopsy to look for cancer cells.
The odds are in your favor: About 95% of thyroid nodules are not cancer. And if it is cancer, it’s likely to be among the most treatable, with a long-term survival rate of about 97%.
If you do have cancer…
Surgery is the main treatment. Most patients will have a total thyroidectomy, the removal of the entire gland. Patients who have this procedure are less likely to have a recurrence of the cancer than those who have just part of the gland removed.
Exception: Some patients with a microcarcinoma—a tumor that is smaller than 1 cm—are good candidates for a lobectomy, the removal of approximately half of the gland.
Radioactive iodine often is given to destroy any thyroid tissue that remains after thyroid surgery, as well as residual microscopic cancer cells. Thyroid tissue is the only tissue in the body that readily absorbs the iodine, which releases radioactivity and kills the cells.
Radioactive iodine has little effect on healthy cells, so patients experience fewer side effects than they might with other forms of radiation treatment. Some patients, however, will experience side effects, such as nausea or dryness of the mouth or eyes. While the side effects will improve over time when the treatments stop—usually after about six weeks—some effects may persist.
Other types of radiation therapy, along with chemotherapy, may be needed for certain types of thyroid cancer or if the cancer has spread.
Supplemental thyroid hormone. Virtually all patients who have had surgery for thyroid cancer will need the medication levothyroxine (Synthroid or Levoxyl, among others) to replace the hormones that were naturally produced by the gland. An additional benefit of levothyroxine is that it suppresses production of thyroid-stimulating hormone (TSH) from the pituitary gland. High TSH levels could stimulate growth of any remaining cancer-producing cells.
