Diagnosis: Anaplastic thyroid cancer ATCDescription: capsuled, septed brown tumor with focal beige necrotic areas.Additional information: minimal invasive thyroid cancer (diameter 10,2 cm) with expanded, not identified anaplastic areas . Half of the tumor consists of undifferentiated spindle cells which are negative for thyroglobuline, TTF-1, CD31, CD34, S100, Calcitonine, Calponine, Desmin, CD68, CD21, Zytoceratine, estrogen receptors and CD117 and focal positive for SMA and 50% positive for progesterone receptors. Morphologically, one can find osteosarcomatous differentiation with osteoid formation.Clinic: 89 year old patient , struma permagna on right side.Increase in height in the past months. Oncocytic neoplasia.