PRIMARY SMOOTH-MUSCLE TUMORS OF THE THYROID-GLAND

BACKGROUND. Primary smooth muscle tumors of the thyroid gland are rare . To date, there are few cases reported of primary thyroid leiomyomas and leiomyosarcomas. METHODS, One leiomyoma and four leiomyosarcomas a rising within the thyroid gland were identified in the files of the En docrine Tumor Registry of the Armed Forces Institute of Pathology. His tologic and immunohistochemical features were reviewed and follow-up o btained. RESULTS. The patients included 2 females, ages 56 and 64 year s, and 3 males, ages 45, 68, and 83 years. The patients presented with a mass in the thyroid gland that had increased in size over a number of months. AU the tumors originated within a single lobe of the thyroi d gland and measured from 1.1 to 9 cm in greatest dimension. Histologi cally, there was a fascicular pattern of growth comprised of spindle-s haped cells with blunt-ended nuclei. The leiomyoma was encapsulated, c ytologically bland, and amitotic; the leiomyosarcomas were invasive wi th increased cellularity, pleomorphism, a high mitotic rate, necrosis, and hemorrhage. Immunohistochemical staining showed reactivity with v imentin, smooth muscle actin, muscle specific actin, and desmin. The p atient with the leiomyoma was alive without evidence of disease 11 yea rs after the initial presentation, with surgical resection as the only treatment. Three of the patients with leiomyosarcomas were dead withi n 2 years of diagnosis, in spite of aggressive therapeutic interventio n. The remaining patient was still alive 10 months after initial prese ntation with multiple lung metastases. CONCLUSIONS. Smooth muscle tumo rs of the thyroid gland are distinctive tumors. Leiomyosarcomas can be distinguished from anaplastic carcinoma, although patient outcome is uniformly unfavorable. (C) 1997 American Cancer Society.