Pituitary carcinoma: An ultrastructural study of eleven cases

Pituitary carcinomas are very rare. Defined as adenohypophysial tumors that undergo craniospinal and/or systemic metastasis, most are PRL- or ACTH-pro ducing. Their ultrastructural features, particularly relative to benign ade nomas of similar functional type, have not been sufficiently explored. Elev en cases of immunohistochemically characterized pituitary carcinoma with do cumented cerebrospinal and/or systemic metastases were collected from vario us institutions and studied by transmission electron microscopy. The tumors were surgically removed from 7 women and 4 men ranging in age between 28 a nd 74 years (mean, 50 years). All were endocrinologically functioning Six t umors secreted PRL; three were ACTH-producing; one each was GH/PRL- and TSH -producing. The patients with the ACTH-producing tumors had all presented w ith Gushing's disease and two of them had undergone adrenalectomy (Nelson s yndrome). In most cases significant cellular atypia and mitotic activity we re observed. In terms of morphologic features of functional differentiation , electron microscopy revealed that in 9 cases the tumor cells maintained a t least some ultrastructural markers of their basic phenotype. A unique fea ture in 2 ACTH carcinomas was the variable admixture of smooth endoplasmic reticulum with intermediate (cytokeratin) filaments. In 2 cases, both PRL-p roducing carcinomas, the cell type comprising the tumor could not be identi fied on an ultrastructural basis alone. Ultrastructural investigation of pi tuitary carcinomas confirms their endocrine nature and, in most but not all cases, reveals their functional differentiation. Despite the diagnostic ut ility of electron microscopy in the assessment of these rare tumors, the di stinction of pituitary carcinoma from pituitary adenoma cannot be firmly ma de on ultrastructural grounds alone.