When cancer metastasizes, bone unwittingly offers a friendly place for tumor cell growth — only to have its hospitality betrayed by pathologic fractures, spinal cord compression, the need for bone surgery or irradiation and an increased risk of death.

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In the largest-known study on bone metastases in thyroid cancer, researchers at the University of Michigan Rogel Cancer Center found that patients with follicular and medullary thyroid cancer had the highest rate of cancer-related bone lesions and fractures and an increased risk of death.

"We know that metastases are bad. But patients in our study who had bone metastases had a worse survival rate compared to patients who had metastases at other distant sites," says Megan Haymart, M.D., assistant professor of medicine at Michigan Medicine and one of the researchers on the study. "This suggests that bone metastases are a uniquely poor prognostic indicator."

But patients with localized or regional thyroid cancer — without metastases — have an excellent prognosis, says Palak Choksi, M.D., assistant professor of medicine at Michigan Medicine and lead author of the study.

The Michigan Medicine study, published in the Journal of Clinical Endocrinology and Metabolism, looked at all forms of thyroid cancer — medullary, follicular, papillary and anaplastic. The study was based on SEER-Medicare data and involved about 30,000 patients, 70 percent of whom were Caucasian women with an average age of 64. The high percentage of women in the study reflects that thyroid cancer is three times more common in women than in men.

"Only about 8 percent of patients in the study had either a bone metastasis or skeletal-related event such as a cancer-related bone fracture," Haymart says.

Helping tailor future treatments

Previous studies that looked mainly at differentiated thyroid cancer and bone metastases had a significantly smaller sample size and were largely from single institutions that enrolled patients with differentiated thyroid cancers.

SEE ALSO: When It's Not Exactly Cancer: Renaming Early Stage Thyroid Tumors

Currently, the data on medications for skeletal metastases in thyroid cancer have been extrapolated largely from breast cancer and other cancers that often metastasize to bone, Choksi says. Little research has focused specifically on the use of medications to treat thyroid cancer with skeletal complications.

"Patients with thyroid cancer have been understudied," Haymart says.

This research will help tailor treatment and management, and it's especially useful for patients with high-risk thyroid cancer (medullary and follicular).

"Now that we have identified that certain thyroid cancers are at a higher risk for skeletal-related events, we can appropriately design studies looking at drugs to see which medication could prevent or effectively treat such complications," Choksi says.

"Through our study, we want other doctors to be aware that there is a higher likelihood of skeletal lesions or fractures in this high-risk population," she says.

The authors acknowledge that the study is limited and that its applicability to younger patients is reduced. "Despite this limitation, our study parallels on a larger scale what other smaller studies have shown in a varied population group," Choksi says.

For high-risk patients, future research is needed to show how to prevent and treat bone metastases. Studies have shown that denosumab and bisphosphonates are beneficial for patients with other cancers of the bone. The researchers suspect these drugs may also benefit patients with thyroid cancer and bone metastases, although additional prospective studies are needed.