After treatment for thyroid cancer, patients may face a slightly increased risk of developing a second primary malignancy elsewhere in the body, research suggests.

Dr. Jonathan D. Tward from University of Utah in Salt Lake City and colleagues investigated the risk of non-thyroid second primary malignancies after differentiated thyroid cancer in more than 30,000 patients diagnosed between 1973 and 2002.

During follow-up ranging from 2 to 359 months, 2158 patients developed second primary malignancies, “significantly more than that expected in the general population,” the investigators report. However, the absolute excess risk was “relatively small at only about 6.5 additional cancers diagnosed per 10,000 persons per year,” Tward told Reuters Health.

There was a significantly increased risk for cancers of the central nervous system, breast, prostate, kidney, Hodgkin lymphoma, leukemia, myeloma, and salivary gland, the investigators report, and a significantly decreased risk for cancers of the head and neck, lung, esophagus, and bladder.

The overall risk of second primary cancers was significantly elevated in the first 10 years after thyroid cancer diagnosis, but not for longer latency periods, the researchers note.

Patients who received radioisotope therapy - which is commonly used to diagnose and treat certain cancers and thyroid disorders - were at increased risk of developing non-thyroid second primary cancers, the investigators say, compared with the general population and with non-irradiated survivors of thyroid cancer.

However, Tward stressed to Reuters Health, that “radioisotope use is a safe and effective therapy whose merits far outweigh the small probability of developing a secondary cancer.”

Results also showed that women in the 25-49 year age group at diagnosis of thyroid cancer had a significantly elevated risk of developing breast cancer, “although the absolute excess risk over these people’s lifetimes was only an additional 4 cases of breast cancer per 10,000 persons per year,” Tward explained.

“Therefore, we would advocate that any woman younger than age 40 at diagnosis perform routine breast self-examination monthly, get an annual breast physical examination by a health care provider, and begin routine, annual screening mammograms within 3 years of their thyroid cancer diagnosis,” he advised.

“Screening in this manner should persist until age 40 where national consensus guidelines such as those of the American Cancer Society or the National Comprehensive Cancer Network would then take over.”

“We would also recommend that all patients under age 40 at diagnosis get annual blood work to screen for hematologic (blood) abnormalities indefinitely,” Tward added.

“The additional risk of prostate cancer, the other malignancy routinely screened for in the United States population, was restricted to men over the age of 50 at the time of their thyroid cancer diagnosis,” he noted. “Therefore, those patients would also fall into screening standards already being implemented in the general population.”

SOURCE: The Journal of Clinical Endocrinology & Metabolism, February 2008.