Thyroid Research Thyroid Research Archive Hypothyroidism

Radiation therapy can cause hypothyroidism in patients with head and neck cancer

(March 2002)

The background of the study. External-beam radiation therapy to the head and neck in young people with Hodgkin's disease is well known to cause thyroid disease, especially hypothyroidism. This study was done to determine the frequency of hypothyroidism in patients with head and neck cancer treated with radiation alone or with radiation and chemotherapy and followed for up to 8 years.

How the study was done. The study subjects were 143 patients (110 men and 33 women) with squamous-cell carcinoma of the head and neck (oral cavity, 6 patients; oropharynx, 68 patients; larynx, 39 patients; hypopharynx, 27 patients; and unknown or multiple sites, 3 patients). The patients were treated with radiation or radiation and chemotherapy. Serum thyrotropin (TSH) was measured before and at the end of treatment, and then at 3- to 6-month intervals. Hypothyroidism was defined as a serum TSH concentration >5.5 µU/mL.

The results of the study. The mean radiation dose to the site of the primary tumor was 6900 cGy (range, 4680 to 8020). The first cases of hypothyroidism were detected 4 months after the initiation of treatment. At 5 years, the incidence of hypothyroidism was 48 percent, and at 8 years it was 67 percent.

There was no relationship between patient age or sex, location of the primary tumor, tumor stage, or radiation dose to the primary site or the neck and the occurrence of hyperthyroidism. Hypothyroidism was equally likely to develop in patients treated with radiation therapy alone and those treated with radiation and chemotherapy.

The conclusions of the study. Patients with squamous-cell carcinoma of the head and neck who are treated with high doses of radiation are at high risk for hypothyroidism.

The original article. Mercado G, Adelstein DJ, Saxton JP, Secic M, Larto MA, Lavertu P. Hypothyroidism: a frequent event after radiotherapy and after radiotherapy with chemotherapy for patients with head and neck carcinoma. Cancer 2001;92:2892-7.