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Histiocytic Sarcoma: Malignant neoplasms composed of MACROPHAGES or DENDRITIC CELLS. Most histiocytic sarcomas present as localized tumor masses without a leukemic phase. Though the biological behavior of these neoplasms resemble lymphomas, their cell lineage is histiocytic not lymphoid.Histiocytic Disorders, Malignant: Distinctive neoplastic disorders of histiocytes. Included are malignant neoplasms of MACROPHAGES and DENDRITIC CELLS.Sarcoma: A connective tissue neoplasm formed by proliferation of mesodermal cells; it is usually highly malignant.Histiocytes: Macrophages found in the TISSUES, as opposed to those found in the blood (MONOCYTES) or serous cavities (SEROUS MEMBRANE).Hyalin: A clear, homogenous, structureless, eosinophilic substance occurring in pathological degeneration of tissues.Splenic Neoplasms: Tumors or cancer of the SPLEEN.Dog Diseases: Diseases of the domestic dog (Canis familiaris). This term does not include diseases of wild dogs, WOLVES; FOXES; and other Canidae for which the heading CARNIVORA is used.Sarcoma, Experimental: Experimentally induced neoplasms of CONNECTIVE TISSUE in animals to provide a model for studying human SARCOMA.Antigens, Differentiation, Myelomonocytic: Surface antigens expressed on myeloid cells of the granulocyte-monocyte-histiocyte series during differentiation. Analysis of their reactivity in normal and malignant myelomonocytic cells is useful in identifying and classifying human leukemias and lymphomas.Dogs: The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)Muramidase: A basic enzyme that is present in saliva, tears, egg white, and many animal fluids. It functions as an antibacterial agent. The enzyme catalyzes the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrin. EC 3.2.1.17.Sarcoma, Ewing: A malignant tumor of the bone which always arises in the medullary tissue, occurring more often in cylindrical bones. The tumor occurs usually before the age of 20, about twice as frequently in males as in females.Sarcoma, Synovial: A malignant neoplasm arising from tenosynovial tissue of the joints and in synovial cells of tendons and bursae. The legs are the most common site, but the tumor can occur in the abdominal wall and other trunk muscles. There are two recognized types: the monophasic (characterized by sheaths of monotonous spindle cells) and the biphasic (characterized by slit-like spaces or clefts within the tumor, lined by cuboidal or tall columnar epithelial cells). These sarcomas occur most commonly in the second and fourth decades of life. (From Dorland, 27th ed; DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1363)Sarcoma, Kaposi: A multicentric, malignant neoplastic vascular proliferation characterized by the development of bluish-red cutaneous nodules, usually on the lower extremities, most often on the toes or feet, and slowly increasing in size and number and spreading to more proximal areas. The tumors have endothelium-lined channels and vascular spaces admixed with variably sized aggregates of spindle-shaped cells, and often remain confined to the skin and subcutaneous tissue, but widespread visceral involvement may occur. Kaposi's sarcoma occurs spontaneously in Jewish and Italian males in Europe and the United States. An aggressive variant in young children is endemic in some areas of Africa. A third form occurs in about 0.04% of kidney transplant patients. There is also a high incidence in AIDS patients. (From Dorland, 27th ed & Holland et al., Cancer Medicine, 3d ed, pp2105-7) HHV-8 is the suspected cause.