Thymic carcinoma with neuroendocrine differentiation in a calf.

A neuroendocrine carcinoma originating in the thymus was found in a 7-month-old, castrated male, Japanese Black calf. The neoplasm consisted largely of very primitive cells, characterized by the paucity of cytoplasmic organelles, but a few cells were immunoreactive for somatostatin or neurofilaments. The expression of both cytokeratin and neurofilament protein was a feature of neuroendocrine differentiation. This neoplasm considered to be a tumor of a thymic stem cell, with little but indubitable evidence of differentiation into somatostatin-producing cells.