Objective: The purpose of our prospective study was to evaluate incidental thyroid cancer diagnosed by screening sonography in a population who underwent breast sonography and the differences in the incidences of thyroid cancer between those with and those without breast cancer.
Subjects and methods: Between January 2003 and March 2004, we examined thyroid glands during routine diagnostic or follow-up breast sonography. A total of 5,549 females underwent breast and thyroid screening sonography (n = 4,864) or sonography for diagnosis or follow-up of breast cancer (n = 685). When a thyroid lesion was suspicious for malignancy, sonographically guided fine-needle aspiration was performed. We compared the cases of pathologically proven thyroid cancer in two groups: a cancer group, including patients with breast cancer, and a noncancer group, including patients with negative or benign breast disease.
Results: Among the 5,549 cases, 42 (0.76%) were diagnosed as thyroid cancer; all were papillary carcinomas. Pathologically proven thyroid cancers were identified in 13 (1.9%) of the 685 breast cancer patients and in 29 (0.6%) of the 4,864 non-breast-cancer patients. The diameters of the 13 thyroid masses were 0.1-3.0 cm; the mean diameters in the cancer and noncancer groups were 9.9 and 8.6 mm, respectively.
Conclusion: The incidence of thyroid cancer was significantly higher in the group with breast cancer than in the group who did not have breast cancer. The results of routine concurrent sonographic breast and thyroid examinations were helpful in detecting small thyroid tumors in both patient groups.