Histiocytic Sarcoma in a Cynomolgus Macaque (macaca Fascicularis) Fed with a High-Fat Diet

Histiocytic sarcoma is characterized by a malignant invasive proliferation of atypical cells showing morphologic and immunophenotypic features similar to those of mature tissue histiocytes. We report a case of histiocytic sarcoma in 11-year-old male cynomolgus macaque fed with a high-fat diet for 6 years. Invasive proliferation of neoplastic cells was localized in systemic organs such as liver, spleen, aorta, kidney, lung, peritonea, and mesenterium. Diffuse cellular foci of invasive proliferation were mainly observed in the peri/intra vascular area, sinus and serous membrane frequently accompanying arteriosclerosis. The tumor cells showed a round to spindle or polygonal shape with abundant foamy to vacuolated cytoplasm. Hemophagocytosis was noted infrequently. In immunohistochemical examinations, some medium to large-sized histiocytic atypical cells were positive for histiocytic markers such as CD68 and Lysozyme. Our case raises the possibility that histiocytic proliferation might be related to hypercholesterolemia and atherosclerosis. This is the first case report of histiocytic sarcoma in non-human primates.