<unk> s are the most common subtype of soft tissue sarcomas, accounting for at least 20% of all sarcomas in adults. Soft tissue sarcomas are rare neoplasms with over 150 different histological subtypes or forms.<unk> s arise from the precursor lipoblasts of the adipocytes (i.e. fat cells) in adipose (i.e. fat) tissues. Adipose tissues are distributed throughout the body, including such sites as the deep and more superficial layers of subcutaneous tissues as well as in less surgically accessible sites like the retroperitoneum (i.e. space behind the abdominal cavity) and visceral fat inside the abdominal cavity. All<unk> s consist of at least some cells that bear a resemblance to fat cells when examined for their histopathologic appearances under a microscope. However, the<unk> s do have several forms based on differences in their clinical presentations (e.g. ages, gender preferences, sites of tumors, signs, and symptoms), severities (i.e. potential to invade local tissues, recur after surgical removal, and metastasize to distal tissues), genetic abnormalities, prognoses, and preferred treatment regimens. The World Health Organization in 2020 reclassified<unk> s into five more or less distinct forms: 1) atypical lipomatous tumor/well-differentiated<unk> ; 2) dedifferentiated<unk> ; 3) myxoid<unk> ; 4) pleomorphic<unk> ; and 5) myxoid pleomorphic<unk> . (Pleomorphic indicates the presence of cells that have abnormal and often large variations in their size and shape and/or the size and shape of their nuclei.) While<unk>  forms are classified as being aggressive and malignant or, in the case of the atypical lipomatous tumor/well-differentiated<unk> , as relatively non-aggressive and benign, all five<unk>  forms can infiltrate locally to injure nearby tissues and organs, occur in surgically inaccessible sites adjacent to vital organs (e.g. the retroperitoneum), recur after surgical removal, and progress to life-threatening diseases. Studies to date find that all five<unk>  forms, while usually treatable at least initially by surgical resection, are often only marginally responsive to currently used chemotherapy and radiotherapy regimens. The<unk> s require a wide range of further studies to determine their responsiveness to various radiotherapy, chemotherapy, and more novel treatment regimens as used individually and in various combinations that would include, where possible, surgical removal.
Liposarcoma
Lipoma
Lipoblastoma
Chondroma
Hemangiosarcoma
Angiosarcoma
Myxoid cyst
Enchondroma