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The Neoplastic Cell Type in Lymphoreticular Neoplasms of the Northern Pike, Esox lucius L.

Department of Zoology, University College, Cork, Ireland; Department of Anatomy and Histology, Royal Veterinary College, S-10405 Stockholm, Sweden; and Laboratory of Pathology, National Cancer Institute, NIH, Bethesda, Maryland 20014

The morphological characteristics of the cells of lymphoreticular tumors in the northern pike (Esox lucius L.) are described. The study was based on light microscopy of sections and imprints subjected to selected staining and histochemical procedures and on electron microscopy of thin sections.

Neoplastic cells from tumors in different individuals as well as within a given tumor were remarkably uniform, highly undifferentiated, and atypical in form. They tended to align themselves in contact with reticulin fibers or capillary walls and were interspersed with histiocytes which often contained phagocytosed nuclear remains.

Nuclei of neoplastic cells were round or slightly indented, with finely dispersed chromatin and a single, fairly large nucleolus. The cytoplasm was moderately abundant and smoothly basophilic and pyroninophilic, except for a juxtanuclear region occupied by a Golgi complex and centrioles. The juxtanuclear regions gave a weakly positive periodic acid-Schiff reaction and a strongly positive acid phosphatase reaction. A few fat droplets were generally present in the cytoplasm.

Free ribosomes, partly in polyribosomal aggregates, were abundant, and mitochondria were numerous. The endoplasmic reticulum was not highly developed, as in typical plasma cells, but occasionally showed configurations suggestive of some protein-secretory activity.

Morphologically, the neoplastic cells seem best classified as atypical hemocytoblasts (stem cells) or immunoblasts. Although limited transmission experiments suggest the possibility of viral etiology, virus particles have not been visualized by thin-section electron microscopy.

¹ Recipient of a research grant from the Irish Cancer Society.

Received 4/27/70. Accepted 7/27/70.