SAN DIEGO — Survivors of breast cancer are at an increased risk for developing thyroid cancer compared with the general population, according to research presented at The Endocrine Society annual meeting.
“Age-specific risk for thyroid cancer is higher among patients with a preceding history of breast cancer,” Jennifer Hong Kuo, MD, of Columbia University Medical Center, New York, said in a press conference. “The risk is highest for patients who are less than 50 years of age when they get diagnosed with their breast cancer.”
Jennifer Hong Kuo
To elucidate the relationship between the two disease processes in a population-based setting, Kuo and colleagues retrospectively analyzed a cohort of patients with breast and thyroid cancer using the Surveillance, Epidemiology and End Results (SEER)-9 database (1973-2011).
“Survival after breast cancer has greatly improved, and we’re now reaching almost 90% at 5 years,” Kuo said. “This means the number of breast cancer survivors in this country is now increasing, and these survivors have an 18% to 30% risk of developing a second cancer.”
The researchers identified 707,678 patients with breast cancer and 52,939 patients with thyroid cancer, and performed analyses using Statistical Package for the Social Sciences software.
After cross-referencing the cohorts, 1,526 patients had developed thyroid cancer after breast cancer, according to Kuo.
The 10-year risk for developing thyroid cancer was higher among patients with breast cancer compared with the general population when stratified by age (16% vs. 0.33% at age 40 years and 12% vs. 0.35% at age 50 years). The risk is reduced as patients get older.
Among breast cancer survivors, thyroid cancer developed at a median of 5 years after their primary diagnosis.
Compared with patients with breast cancer only, those who developed secondary thyroid cancer were younger (54 ± 0.31 vs. 61 ± 0.01 years, P < .0001) with smaller breast cancers (15 ± 0.52 mm vs. 18 ± 0.03 mm, P < .001); patients showed no difference in estrogen receptor/progesterone receptor positivity or lymph node involvement.
“These patients have smaller tumors, and there’s a greater percentage of invasive ductal carcinoma,” Kuo said. “A greater number of these patients receive adjuvant radiation therapy.”
The proportion of patients with a second cancer who received adjuvant therapy was 47.9% compared with 44% with breast cancer only (P = .021) based on univariate analysis, but the results lost significance on multivariate analysis.
“Adjuvant radiation therapy is associated with the development of a second primary thyroid cancer, but is not in and of itself an independent predictor for the development of thyroid cancer,” Kuo said. “This is probably reflective of the surgical treatment these patients receive.”
Compared with thyroid cancers in the general population, a greater proportion of patients with both cancers demonstrated tall cell, oxyphilic, follicular and anaplastic variants.
Although these are generally more aggressive forms, Kuo noted the tumors tend to be smaller, with fewer patients receiving radioactive iodine ablation.
“This study supports that breast cancer survivors are at a higher risk for thyroid cancer,” Kuo said. “This should promote awareness for those physicians who are taking care of this patient cohort.” – by Allegra Tiver
Kuo JH. Poster Board THR-049. Presented at: The Endocrine Society Annual Meeting; March 5-8, 2015, San Diego.
Disclosure: Kuo reports no relevant financial disclosures.