New technique for thyroid cancer therapy eliminates many side effects

Differentiated thyroid cancer, the most common form of thyroid cancer, is one of the success stories in the war on cancer. Since the advent of radioiodine therapy, it has been considered one of the most curable cancers. On the downside, current treatment involves taking patients off their thyroid medication. This can lead to serious side effects including symptoms of hypothyroidism, an unbalanced metabolic state that can induce fatigue, depression, and other unpleasant conditions.

Bart de Keizer, MD, and a team from the University Medical Center in Utrecht, The Netherlands, and Ghent University Hospital, Belgium, reported in the September issue of The Journal of Nuclear Medicine, on a new technique that allows patients to maintain their normal course of thyroid medication prior to and during radioiodine therapy. The new technique avoids the problems of hypothyroidism, and levels of radiation in the blood and bone marrow remain well below the accepted safety thresholds during therapy.

Currently, thyroid cancer patients who have had their thyroid removed are treated with radioactive iodine, which effectively zeros in on and kills any remaining cancerous thyroid cells. But prior to radioiodine treatment, the patient must be taken off thyroid hormone replacement medication for up to 6 weeks. The withdrawal of thyroid medication signals the body to produce thyroid stimulating hormone (THS). TSH causes any remaining or metastasized thyroid cells to quickly absorb the radioactive iodine when it is administered, in effect forcing the cancerous cells to absorb lethal radioactive molecules that are largely ignored by other cells in the body.

By using a genetically engineered version of the natural hormone (recombinant human thyroid stimulating hormone [rhTSH]) instead of thyroid medication withdrawal to stimulate the cancerous cells to quickly take up the radioactive iodine, the research team in The Netherlands and Belgium found that the problems of hypothyroidism can be avoided. This new technique may also increase the safety of radioiodine treatment and may allow a higher, more effective dose of radioiodine to be used when needed. That’s because when the body is not in a state of hypothyroidism, it can more efficiently process and excrete any radioiodine that hasn’t been absorbed.

The study, which involved 14 patients and 17 treatments, showed that treatment with rhTSH was well tolerated. None of the patients showed blood toxicity, and no bone marrow-related side effects were noted. Blood and bone marrow are the tissues most sensitive to radiation. As expected, none of the patients showed symptoms of hypothyroidism during or following treatment.

According to Dr. de Keizer, “Using rhTSH before administering radioiodine treatments resulted in no clinically relevant side effects. Therefore, although further testing needs to be done, our findings imply this treatment should improve efficacy while preserving safety and tolerability of treatment.”