03.10.2015 Staff Writer, MedPage TodaySAN DIEGO -- Breast cancer survivors may have a higher risk of developing thyroid cancer compared with the general population, researchers reported here. The association was stronger for younger breast cancer survivors, Jennifer Hong Kuo, MD, of Columbia University in New York City, and colleagues reported at The Endocrine Society annual meeting. ADVERTISEMENTKuo said clinicians should be vigilant about surveillance of their breast cancer patients for thyroid cancer and that these patients should be informed about their potentially higher risk. Jason Wexler, MD, of Washington Hospital Center in Washington, who was not involved in the study, said it's not clear that all breast cancer patients should be screened for thyroid cancer yet. "But I do think it's important that we identify these patients as requiring careful follow-up beyond their treatment and the resolution of their primary malignancy," Wexler said during a press briefing. "This cohort may require lifelong surveillance, and perhaps we should enlighten the primary care world about that, since these patients might not find their way to endocrinologists." Kuo said survival rates following breast cancer are improving, and are now approaching 90% at 5 years. But some studies have shown that these women may be at risk of developing secondary cancers, although much of this evidence is based on lower quality, single-center studies. To further investigate this potential link, Kuo and colleagues looked at data from the Surveillance, Epidemiology, and End Results Database (SEER-9) from 1973 to 2011. They included a total of 707,678 patients with breast cancer; 1,526 of these women had subsequent thyroid cancer. Kuo and colleagues found that breast cancer survivors had higher rates of developing thyroid cancer than the general population, if they were younger: Age 40: 16% versus 0.33% Age 50: 12% versus 0.35% This association, however, was not seen for older women. Kuo noted that the median time to development of a thyroid cancer was 5 years, suggesting the need for surveillance especially within that time period. Her group also found that breast cancer survivors who develop thyroid cancer have smaller tumors, and have a greater percentage of invasive ductal carcinoma. Adjuvant radiation therapy was also associated with the development of thyroid cancer (OR 0.70, 95% CI 0.62-0.78, P<0.001), but in further analyses it was not an independent predictor of developing thyroid cancer. "I think it contributes, but it doesn't explain the whole story," Kuo said, noting that younger patients are more susceptible to the effects of radiation therapy. "You'd expect to see papillary thyroid cancers, which are associated with radiation effects. But when you compare thyroid cancers in these patients versus the general population, you find a greater percentage of tall cell and other variants." Kuo said that the association needs further study in order to more fully elucidate other factors that could contribute to it.
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