According to recent results published in the journal Cancer, hypothyroidism frequently occurs in patients with head and neck cancer after treatment with radiation.

The term head and neck cancer refers to any number of cancers that may occur in the head and/or neck region. These may include cancers of the tongue, mouth, salivary glands, pharynx, larynx, sinus and other sites located in the head and neck area. If the cancer is locally advanced (has spread to nearby tissue or lymph nodes), surgery alone may not be curative. Nonetheless, the patient may elect surgery to remove as much of the cancer as possible. Following surgery, the patient may then undergo radiation therapy or combination radiation/chemotherapy treatment in an attempt to destroy remaining cancer cells.

Radiation treatment is well recognized as a cause of hypothyroidism. The thyroid is a gland located in the neck near the windpipe that produces hormones, including thyroid-stimulating hormone (TSH), needed for the function of the body’s cells. Thyroid hormones help regulate growth and metabolism. Hypothyroidism occurs when the thyroid is producing abnormally low levels of thyroid hormones and can result in a variety of symptoms. In general, hypothyroidism slows the body’s normal rate of functioning, causing mental and physical sluggishness that can range from mild to life-threatening.

Researchers at the Cleveland Clinic Foundation conducted a trial evaluating the incidence of hypothyroidism in 143 patients treated for head and neck cancer. Approximately one-third of the patients were treated with radiation to the neck area while the other two-thirds received radiation with concurrent chemotherapy. For an average of 4.4 years after treatment, all patients were tested at regular intervals for blood levels of TSH.

Using statistical models, researchers were able to project that 48% of the patients would experience hypothyroidism five years after treatment, with that number jumping to 67% eight years after treatment. The average time to development of hypothyroidism was 1.4 years, but ranged from .3 to 7.2 years. Importantly, there was no difference in risk for developing hypothyroidism between patients treated with radiation alone or those treated with radiation and chemotherapy. The only factor that could predict whether or not an individual would develop hypothyroidism was race: none of the African-American patients developed hypothyroidism.

This study indicates that the incidence of hypothyroidism among head and neck cancer patients treated with radiation is higher than previously reported and that TSH screening should be conducted at regular intervals for extended periods of time after completion of treatment. (Cancer, Vol 92, Issue 11, pp 2892-2897, 2001)