SUN-476 Risk of Thyroid Cancer in McCune-Albright Syndrome

Background: McCune-Albright syndrome (MAS) is a well described genetic syndrome characterized by café-au-lait spots, polyostotic fibrous dysplasia, and hyperfunctioning endocrinopathies. Hyperthyroidism is a common endocrine manifestation of MAS, but thyroid nodules are less frequently observed. Thyroid cancer is generally considered uncommon in patients affected by MAS. Clinical Case: A 15-year-old male was referred to endocrinology for evaluation of polyostotic fibrous dysplasia with onset at 6 years old. He had no café-au-lait spots and initial labwork revealed no endocrine abnormalities. Subsequent labwork revealed non-autoimmune hyperthyroidism, leading to a diagnosis of MAS. Repeat clinical assessment revealed a goiter. 123-I uptake and scan revealed diffusely increased uptake throughout the gland with increased intensity in two regions of the right lobe separated by a region of photopenia. Ultrasound demonstrated three right-sided thyroid nodules – two correlating with the areas of increased iodine uptake and one with the area of photopenia. The left lobe of the thyroid was normal. FNA biopsy was performed and cytopathology was consistent with Bethesda II and III for the hyperfunctioning nodules and Bethesda VI for the cold nodule. The patient received total thyroidectomy with right-sided central neck dissection, and he was found to have multiple foci of papillary thyroid carcinoma with central neck metastases. The largest hyperfunctioning thyroid nodule was benign. He received radioactive iodine ablation which demonstrated no distant metastases and has had no evidence of recurrent disease. Conclusions: Hyperthyroidism is a common manifestation of MAS, but thyroid nodules are much less frequently observed, and thyroid cancer is considered quite rare. This patient developed TSH-independent hyperthyroidism in normal thyroid cells as well as in two hyperfunctioning thyroid nodules. He developed two contemporaneous classical papillary thyroid cancers – one manifesting as a nonfunctioning thyroid nodule and one manifesting as a thyrotoxic nodule with lymphatic invasion. We conclude that individuals with MAS may be at an increased risk for thyroid nodules and thyroid cancer, although the data are not well established. Clinicians should have a low threshold for thyroid ultrasound in patients with MAS and goiter. Reference: (1) Collins, M. T., Sarlis, N. J., Merino, M. J., Monroe, J., Crawford, S. E., Krakoff, J. A., Guthrie, L. C., Bonat, S., Robey, P. G., & Shenker, A. (2003). Thyroid carcinoma in the McCune-Albright syndrome: contributory role of activating Gsα mutations. The Journal of Clinical Endocrinology & Metabolism, 88(9), 4413-4417. (2) Hannon, T. S., Noonan, K., Steinmetz, R., Eugster, E. A., Levine, M. A., & Pescovitz, O. H. (2003). Is McCune-Albright syndrome overlooked in subjects with fibrous dysplasia of bone?. The Journal of pediatrics, 142(5), 532-538.