Genetically engineered thyroid stimulating hormone destroys tissue that often remains after thyroidectomy

Jun 16 2004

Using a genetically engineered thyroid stimulating hormone (TSH) - called thyrotropin alfa, or rTSH - doctors were able to ablate, or destroy, the small amount of thyroid gland tissue that often remains after thyroidectomy, without the need to temporarily withhold thyroid hormone medication. This new approach also avoided the temporary but troubling symptoms flowing from the deficiency of thyroid hormone (or hypothyroidism), such as fatigue, weight gain, chilliness, slowed thinking, depression, constipation and muscle cramps.

The findings will be highlighted during the clinical trial symposium at the 86th annual meeting of The Endocrine Society in New Orleans, June 16-18.

"Recovery from thyroid cancer has been very difficult for patients because thyroid medication - to replace the thyroid hormone naturally produced by a healthy thyroid gland - has traditionally been withheld for four to six weeks after surgery so radioiodine could be used to identify and destroy glandular tissue that remained," said study co-lead investigator Paul Ladenson, M.D., professor and chief of the Division of Endocrinology at the Johns Hopkins School of Medicine.

The study - at nine centers in North American and Europe - examined 63 patients with thyroid cancer, all of whom had thyroid removal surgery and were undergoing post-operative radioiodine therapy to ensure that all tissue was destroyed. This procedure, called remnant ablation, lowers the risk of thyroid cancer recurrence for some patients and makes for more accurate testing to detect it when it does return. It uses radioactive iodine to ablate remaining tissue and has previously required withholding of replacement thyroid hormone to allow the patient's own levels of TSH to rise, stimulating thyroid tissue to take up the radioiodine that destroys it.

Each participant was assigned to either an experimental group or a control group. Participants in the experimental group received thyrotropin alfa while taking hormone replacement therapy to maintain a normal thyroid state. For those in the control group, hormone replacement therapy was withheld for the usual four-to-six weeks after surgery, sending them into hypothyroidism. All patients subsequently received radioiodine therapy to wipe out any remaining glandular tissue. Repeat radioiodine scans and thyroglobulin blood tests were performed eight months after surgery to assess the effectiveness of the two approaches.

For both study groups, radioiodine ablation was effective in 75 percent to 100 percent of patients - destroying all thyroid tissue, based on three different criteria. As the researchers expected, patients whose hormone therapy was withheld experienced more symptoms of hypothyroidism than patients who received the thyrotropin alfa.

"The advantage of thyrotropin alfa is that patients can remain on thyroid hormone medication while undergoing testing and not experience the symptoms of hypo-thyroidism," said Ladenson. "These results indicate that thyroid cancer patients can be treated effectively without the very unpleasant side effects that have previously been associated with temporarily withholding their thyroid hormone treatment after surgery."

The thyroid gland is located in the lower front part of the neck. It produces important hormones that the body needs to function normally. The American Cancer Society estimates that in 2004, about 23,600 new cases of thyroid cancer will be diagnosed in the United States. It is three times more common in women than in men. Most cases are discovered during a routine physical examination when a painless lump is found in the thyroid.