Dendritic Cell Sarcoma, Follicular: Sarcoma of FOLLICULAR DENDRITIC CELLS most often found in the lymph nodes. This rare neoplasm occurs predominately in adults.Dendritic Cell Sarcoma, Interdigitating: A rare sarcoma of INTERDIGITATING CELLS found in the lymph nodes and non-lymphoid organs. They exhibit a variable immunophenotype and lack Birbeck granules.Sarcoma, Clear Cell: A sarcoma of young, often female, adults of the lower extremities and acral regions, intimately bound to tendons as circumscribed but unencapsulated melanin-bearing tumors of neuroectodermal origin. An ultrastructural finding simulates flattened and curved barrel staves, corresponding to the internal structures of premelanosomes. There is a 45-60% mortality in clear cell sarcoma. (Segen, Dictionary of Modern Medicine, 1992)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.Langerhans Cell Sarcoma: Rare malignant neoplasm of dendritic LANGERHANS CELLS exhibiting atypical cytology, frequent mitoses, and aggressive clinical behavior. They can be distinguished from other histiocytic and dendritic proliferations by immunohistochemical and ultrastructure studies. Cytologically benign proliferations of Langerhans cells are called LANGERHANS CELL HISTIOCYTOSIS.Dendritic Cells, Follicular: Non-hematopoietic cells, with extensive dendritic processes, found in the primary and secondary follicles of lymphoid tissue (the B cell zones). They are different from conventional DENDRITIC CELLS associated with T-CELLS. They are derived from MESENCHYMAL STEM CELLS and are negative for class II MHC antigen and do not process or present antigen like the conventional dendritic cells do. Instead, follicular dendritic cells have FC RECEPTORS and C3B RECEPTORS that hold antigen in the form of ANTIGEN-ANTIBODY COMPLEXES on their surfaces for long periods for recognition by B-CELLS.Sarcoma: A connective tissue neoplasm formed by proliferation of mesodermal cells; it is usually highly malignant.Dendritic Cells: Specialized cells of the hematopoietic system that have branch-like extensions. They are found throughout the lymphatic system, and in non-lymphoid tissues such as SKIN and the epithelia of the intestinal, respiratory, and reproductive tracts. They trap and process ANTIGENS, and present them to T-CELLS, thereby stimulating CELL-MEDIATED IMMUNITY. They are different from the non-hematopoietic FOLLICULAR DENDRITIC CELLS, which have a similar morphology and immune system function, but with respect to humoral immunity (ANTIBODY PRODUCTION).Sarcoma, Small Cell: A sarcoma characterized by the presence of small cells, cells measuring 9-14 micrometers with a faint or indistinct rim of cytoplasm and an oval-to-elongated nucleus with relatively dense chromatin. (From Segen, Dictionary of Modern Medicine, 1992)Cell Transdifferentiation: A naturally occurring phenomenon where terminally differentiated cells dedifferentiate to the point where they can switch CELL LINEAGES. The cells then differentiate into other cell types.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)Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Soft Tissue Neoplasms: Neoplasms of whatever cell type or origin, occurring in the extraskeletal connective tissue framework of the body including the organs of locomotion and their various component structures, such as nerves, blood vessels, lymphatics, etc.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, Experimental: Experimentally induced neoplasms of CONNECTIVE TISSUE in animals to provide a model for studying human SARCOMA.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.Avian Sarcoma Viruses: Group of alpharetroviruses (ALPHARETROVIRUS) producing sarcomata and other tumors in chickens and other fowl and also in pigeons, ducks, and RATS.Sarcoma 180Oncogene Proteins, Fusion: The GENETIC TRANSLATION products of the fusion between an ONCOGENE and another gene. The latter may be of viral or cellular origin.Nephroma, Mesoblastic: A solid, unencapsulated tumor of the KIDNEY composed of spindle mesenchymal cells that resemble FIBROBLASTS or muscle cells. The homogeneous mass typically extends into the renal parenchyma and replaces most of the kidney. In most cases, mesoblastic nephroma is benign and occurs in the fetus or newborn, and rarely in the older child or the adult.Lymphoma, Non-Hodgkin: Any of a group of malignant tumors of lymphoid tissue that differ from HODGKIN DISEASE, being more heterogeneous with respect to malignant cell lineage, clinical course, prognosis, and therapy. The only common feature among these tumors is the absence of giant REED-STERNBERG CELLS, a characteristic of Hodgkin's disease.