Background: A breast cancer (BC) history was elicited more frequently than expected among thyroid operation patients, which prompted an investigation of risks for concurrent or subsequent nonendocrine malignancies. Methods: Of 94,939 patients at a tertiary referral center with breast, thyroid, or parathyroid disease from 2000 to 2006, those patients with more than one tumor type were identified. Rates of BC, thyroid cancer (TC), hyperparathyroidism (HPT), and multiple diagnoses were compared with matched populations using Surveillance, Epidemiology, and End Results (SEER) data. Results: Of those patients identified, 1604 patients had TC, 12,440 patients had BC, and 1352 patients had HPT. Sixty patients with TC (3.7%) and 70 patients with HPT (5.2%) also had BC. Of 820 consecutive thyroidectomy patients, 23 patients (2.8%) had TC and BC, compared with 1.6% expected from a Monte Carlo distribution using SEER data (P = .001). BC and TC occurred within 5 years in 90% of patients, who tended to be older than those with a single cancer. HPT affected 0.6% of patients with BC, 6% of patients with TC, and 7% of patients with both malignancies. Conclusion: Patients found initially to have TC or BC may be predisposed to develop the other malignancy within a short timeframe. HPT is also more prevalent among these patients. Vigilant screening for associated disorders should accompany initial diagnosis of either cancer.
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