Simultaneous diagnosis of papillary thyroid cancer and systemic mastocytosis.

Key Clinical Message: When managing patients with differentiated thyroid cancers (DTC) and lytic bone lesions, physicians should consider etiologies other than DTC bony metastases when there is no biochemical and functional radiographic evidence of extensive DTC burden. Systemic mastocytosis (SM) is a clonal expansion of mast cells associated with an increased risk of solid malignancies. There is no known association between systemic mastocytosis and thyroid cancer. We report a young woman who presented with cervical lymphadenopathy, palpable thyroid nodule, and lytic bone lesions who was diagnosed with papillary thyroid cancer (PTC). The patient's post‐surgical thyroglobulin was lower than expected for metastatic thyroid cancer, and the lytic bone lesions did not demonstrate uptake of I123. Upon further evaluation, the patient was found to have SM. We report a case of co‐occurrence of PTC and SM. [ABSTRACT FROM AUTHOR]