[Spindle-cell variant of thyroid medullary carcinoma with favourable prognosis].

A case of a favourable outcome of spindle-cell medullary carcinoma of the thyroid is reported. Electron-microscopically, there was no correlation between histological and ultrastructural differentiation. The tumor consisted mainly of ultrastructurally differentiated cells with endocrine granules which may be the cause of the favourable prognosis.