Rare Spontaneous Proliferating Tumour in Rat: Fibrosarcoma
A 1 year old, male Wistar rat presented to clinic having a subcutaneous greyish-white mass extending to the supraorbital area of the left eye. The stained impression-smear in the microscope small field showed bunches of round cells in diffused masses, which were present in various stages of cell division. Large numbers of cells were present in the mitosis phase. Large populations of neoplastic spindle cells, rare pleomorphic multinucleated cells, and rare leukocytes were observed. The primary tumour was characterized by fusiform spindle cells producing various amounts of interlacing bundles of collagen. The spindleshaped cells contained moderate amounts of eosinophilic, fibrillar cytoplasm with an oval nucleus, coarsely clumped chromatin, and one or more nucleoli. Some of the round cells were present in the nucleolar remoulding stage and the presence of immature proliferating cells had previously been identified as spindle cell fibrosarcomas. During progression, the tumour acquires self-dependence and the ability to invade other tissues and metastasize. The primary tumour was characterized by fusiform spindle cells producing various amounts of interlacing bundles of collagen. The cells formed a characteristic herringbone pattern and mitotic figures were frequent. The relationship to human fibrosarcoma is noted.