Malignant lymphoma resembling Burkitt's tumour in rhesus monkeys: (light- and electron microscopic studies)

Spontaneous tumours of the haematopoetic system have been only rarely observed in nonhuman primates. We had the opportunity to carry out light and electron microscopic investigations of three lymphomas in immature rhesus monkeys from our colony. All animals had tumours of both retroperitoneum and lymph nodes. The relatively uniform lymphoblastic or lymphoreticular tumour cells as well as the massive occurence of the so-called "starry sky macrophages" were histologically characteristic. Histochemically, the marked pyroninophilia of these tumour cells was evident. The electron nicroscopy revealed the tumour cells as lymphoblasts of about 8 mu diameter with the following features: round or oval, occasionally deeply indented cell nuclei with relatively clear interchromatinic substance; mostly well developed nucleoli; sparsely, rough endoplasmatic reticulum; large numbers of free ribosomes and polyribosomes; a few large, bizzarre mitochondria, often situated at one pole; lipid vacuoles in some cells. These histological, cytological and electron microscopic characteristics correspond to those of the human Burkitt's Lymphoma. This tumour is classified as an undifferentiated malignant lymphoma. Tumours of this type are of particular interest on comparative and epidemiological reasons in light of the existence of morphologically similar experimental, virus induced lymphomas in monkeys.