Overuse of Radioactive Iodine: article in the Journal CANCER

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Doctors overusing thyroid cancer treatment: study

Fri, Apr 15 2011

By Genevra Pittman

NEW YORK (Reuters Health) - Too many patients are getting a thyroid cancer treatment that kills thyroid tissue but can also harm other tissues in the process, according to a new study.

The research, published in Cancer, finds that doctors are treating patients with early-stage, low-risk thyroid cancer using radioactive iodine, which doesn't increase their chances of surviving but may put them at risk for a secondary cancer.

"Our study shows that these low-risk patients do not need" radioactive iodine, Dr. Ian Ganly, one of the study's authors from Memorial Sloan-Kettering Cancer Center in New York, told Reuters Health.

"Therefore there is no need to expose these patients to any risk from (radioactive iodine) treatment," he said in an email.

Guidelines from the American Thyroid Association say that radioactive iodine, taken as a pill or in a drink, should be used selectively and in patients with intermediate and high-risk thyroid tumors. In those patients, the treatment helps prevent the cancer from coming back after surgery, Ganly said.

But there is no evidence that radioactive iodine helps patients with very small, low-risk tumors, the authors say, and these types of tumors are being diagnosed more frequently in the U.S. as cancer detection improves.

Surgery to remove part of the thyroid or the entire thyroid is usually enough to cure patients with low-risk tumors, according to the American Cancer Society.

To study the way doctors prescribe radioactive iodine and the treatment's effects in low-risk patients, the authors consulted a nation-wide database of about 37,000 cases of thyroid cancer diagnosed between 1973 and 2007.

In total, close to 15,000 of those patients were treated with radioactive iodine, and just over 3,000 patients developed secondary cancers over an average follow-up period of 11 years.

Radioactive iodine became more popular in patients with low-risk tumors over the course of the study period. Early on, only about 3 percent of those with small tumors were treated with radioactive iodine, compared to 38 percent in recent years.

The authors calculated that the radioactive iodine was not responsible for any secondary cancers at the beginning of the study, but was to blame for about 14 extra cancers per 10,000 patients in a given year by the end of the study.

Cancer of the salivary gland - where radioactive iodine may accumulate - as well as leukemia were more common in patients who had been treated with radioactive iodine.

Ganly said the risk of leukemia may increase because radioactive iodine circulates in the blood, thus exposing bone marrow to its tissue-killing effects.

Because the treatment hasn't been shown to benefit patients with low-risk thyroid cancer, any extra risk, even a tiny one, isn't worth it, Ganly said.

He said that more doctors need to be aware of guidelines that limit the use of radioactive iodine to those patients for whom the benefits clearly outweigh the risks.

"I think this is due to lack of knowledge or lack of understanding from treating physicians," Ganly said.

Dr. Sisson, who studies thyroid disease at the University of Michigan, said that the guidelines on radioactive iodine may not be specific enough, leading too many doctors to decide that their patients might qualify for the treatment.

And with more and more tiny cancers being diagnosed, he said, "If you start treating patients with this microscopic evidence of thyroid cancer, you don't know where to stop."

Sisson, who was not involved in the current study, said that while the findings illustrate a real problem in the treatment of thyroid cancer, it's not clear that problem is going to be fixed anytime soon.

"It's an important paper, but I would believe that it would have a modest impact," he told Reuters Health. "There's been a great reluctance on the part of practitioners to change their practice."

Recently, Sisson said, "there is some change in attitude, but not much."

SOURCE: bit.ly/hwSqDz Cancer, online March 22, 2011.