Rare incidence of spontaneous malignant fibrous histiocytoma in the rhesus monkey

The rodents are being widely used for cancer research studies, however, being phylogenetically distant; rodents do not closely mimic the disease progression as in humans. Therefore, Non-human Primates (NHPs) which are genetically closer to human are evidently better models. The outcome of preclinical tumor studies on NHPs has greater applicability in humans than those on rodents. The incidence of spontaneous neoplasia in NHPs is rare. We observed a case of spontaneously occurring tumor located at the lateral side of the neck adjacent to the shoulder joint in an adult rhesus monkey. The tumor arose as subcutaneous reddish-white mass, multicentric firm, and pedunculated smooth nodules with tall warty growths, resembling cauliflower in appearance. Microscopically, five different types of pleomorphic cells such as fibroblast-like cells, histiocyte-like cells, undifferentiated cells, xanthomatous cells, and multinucleated giant cells were observed. All cells were of storiform pattern, with irregular fascicles and variable cellularity, including atypical forms with numerous mitotic figures, which was suggestive of Malignant Fibrous Histiocytoma (MFH). The study of such spontaneous tumors may assist researchers in developing animal cancer models for human malignancies and, owing to their similarity with human cancers, help in prevention and treatment.