Thyroid Cancer Risk Increased After Breast Cancer

SAN DIEGO — The risk for developing thyroid cancer appears to be higher in breast cancer survivors, especially among those aged younger than 50 years with invasive ductal carcinoma, new data presented at ENDO 2015 suggest.

“Although the incidence of breast cancer has been somewhat stable over the last couple of decades, it is still a leading cause of cancer and affects 1 in 8 women in this country sometime in their lifetime,” study researcher Jennifer Kuo, MD, assistant professor of surgery at Columbia University in New York City, said during a press conference.

This means, she noted, that the number of breast cancer survivors has increased substantially. However, these survivors have an 18% to 30% increased risk for developing a second cancer. Although these second cancers are usually hormonally mediated, such as ovarian or uterine cancers, some studies have suggested that incidence of thyroid cancer is also increased in this patient population.

To investigate the potential relationship between breast cancer and second primary thyroid cancer, Dr. Kuo conducted a retrospective cohort analysis of the Surveillance, Epidemiology, and End Results (SEER)-9 database. Specifically, she looked at the years from 1973 to 2011.

Dr. Kuo identified more than 700,000 patients with breast cancer and just under 50,000 with thyroid cancer. She then cross-referenced these two patient cohorts and found about 1,500 patients who developed thyroid cancer after breast cancer. Patients who had breast cancer only and those who had thyroid cancer only were then compared.

Dr. Kuo calculated age-specific 10-year risk for developing thyroid cancer after breast cancer and compared it with the age-specific 10-year risk published by the SEER database.

Results indicated that median time to development of second primary thyroid cancer was 5 years. When compared with patients who had breast cancer only, those who developed thyroid cancer after breast cancer were younger when they received their breast cancer diagnosis (aged 50 years or younger); had smaller tumors; and had a greater percentage of invasive ductal carcinoma.

Further, a greater percentage of these patients received adjuvant radiation therapy. The significance of this finding, however, dropped on multivariable analysis.

“I don’t necessarily think that radiation therapy is not significant. When put all together, these younger patients with smaller invasive cancers are more likely to be treated with breast conservation therapy, which is only possible with radiation therapy, so that kind of fits the picture,” Dr. Kuo said.

However, she noted that radiation therapy is likely not fully responsible for the development of thyroid cancer in breast cancer survivors.

“Although I think radiation therapy does contribute to this story, it doesn’t completely explain the whole story. You would expect that, if this was completely due to radiation, that the thyroid cancers would be predominantly papillary thyroid cancer, which we know is associated with radiation effects,” Dr. Kuo said.

“But actually, when we compare the thyroid cancers in these patients to the thyroid cancers in the general population, we find a greater percentage of tall cell variant papillary thyroid cancer, oxyphilic follicular thyroid cancer and anaplastic thyroid cancers — all of which are generally more aggressive forms of thyroid cancers.”

She added, however, that these cancers tend to be smaller, and the patients receive less radioactive iodine ablation and therefore still have a very good prognosis.

“This study supports the fact that breast cancer survivors are at a higher risk for thyroid cancer, and this should promote a greater awareness of this risk for those physicians who are taking care of this patient cohort,” Dr. Kuo concluded.

Reference

1. Kuo J. Abstract THR-049. Presented at: The Endocrine Society’s 97th Annual Meeting & Expo (ENDO 2015); March 5-8, 2015; San Diego.