Radiation Exposure, Including in Workplace, Worsens Outcome in Thyroid Cancer

Nick Mulcahy

April 21, 2009

April 21, 2009 — Thyroid cancer patients with exposure to radiation — from healthcare workplaces, for example, or treatments for conditions such as breast cancer and acne — appear to have worse outcomes than patients with the disease and no exposure.

"Radiation exposure is a well-established risk factor for thyroid cancer," write the study authors, led by senior author Jeremy L. Freeman, MD, otolaryngologist-in-chief at Mount Sinai Hospital, in Toronto, Ontario, in a study published in the April issue of the Archives of Otolaryngology — Head & Neck Surgery.

However, previous studies of thyroid cancer patients have shown no difference in clinical outcome between those exposed to radiation and those not exposed.

The new study retrospectively reviewed 125 Mount Sinai patients with radiation exposure and compared them with a database of 574 Mount Sinai patients with no exposure.

Dr. Freeman and colleagues found that, compared with patients with no exposure, radiation-exposed patients were more likely to have stage IV disease, and thus distant metastases (9% vs 2%), and to have died (4% vs 1.5%) — which is in contrast to previous reports comparing the 2 groups, say the authors. Also, more exposed patients underwent total or near-total thyroidectomy (83% vs 38%). Further, more of the exposed patients required additional procedures (23% vs 2%), which is also in contrast to previous findings.

"To our knowledge, the present study is the first to suggest worse prognosis in radiation-exposed patients," write the authors, who speculate that the relatively large number of exposed patients in the study might account for the differences with other research.

The present study is the first to suggest worse prognosis in radiation-exposed patients.

The tumors of radiation-exposed patients also had more aggressive pathology, write the authors, with more multifocal disease (63% vs 36%) and extrathyroid spread (26% vs 8%) than patients without exposure.

Most of the patients in the study (56%) had exposure to radiation from direct external radiotherapy to the head and neck, "often as therapeutic radiography to treat benign conditions," such as acne, write the authors. "A whole bunch of people in the 1950s and 60s were given radiation for acne, adenoids, fungal infections, and other conditions," Dr. Freeman told Medscape Oncology. "The people who received that radiation are paying for it in later life," he said.

A whole bunch of people in the 1950s and 60s were given radiation for acne, adenoids, fungal infections, and other conditions.

The second-most common type of exposure (23%) was occupational/diagnostic, which includes unprotected radiography technicians, dental assistants, and patients who had repeated imaging of the head and neck. "The people in this group include technicians who ran fluoroscopes and dental and x-ray technicians who did not leave the room or wear protection," said Dr. Freeman, who explained that the state of the art in the 1950s and 1960s did not understand the ramifications of these exposures.

Environmental exposure (including the accident at Chernobyl) accounted for 11% of the patients. Direct external radiotherapy to another body site, such as the breast, accounted for 6%.

Radiotherapy to Head and Neck Most Damaging

Most patients with well-differentiated thyroid cancer have good disease-specific outcomes, write the authors. Indeed, even among these radiation-exposed patients, who were followed for a mean of 10.6 years, most patients (86%) were alive and free of disease at last follow-up.

However, in an effort to determine whether the type of previous radiation exposure had an effect on tumor pathologic findings or clinical outcome, the researchers divided the radiation-exposed patients into subgroups according to type of exposure.

These subgroups were compared for age at exposure, cancer stage, MACIS (metastasis, age, completeness of resection, invasion, and size of tumor) score, local recurrence, distant metastases, and likelihood of death from disease.

Notably, the subgroup exposed to direct external radiotherapy to the head and neck accounted for 56% of all patients with stage IV disease and 60% of all patients with MACIS scores higher than 8. Also, this subgroup accounted for 63% of patients who experienced local recurrence, 55% of those with distant metastases, and 80% of those who died of thyroid cancer. This patient subgroup also had the most patients.

Also, these patients had radiation exposure at a statistically significant younger age (mean age, 14.9 years) than each of the other subgroups (< .005), except the group exposed either occupationally or through diagnostics (mean age, 19.9 years). "The young age here probably largely represents treatment for acne," said Dr. Freeman about the head and neck subgroup.

The researchers have disclosed no relevant financial relationships.

Arch Otolaryngol Head Neck Surg. 2009;135:355-359.

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