Alveolar soft part sarcoma, abbreviated ASPS, is a very rare type of soft-tissue sarcoma, that grows slowly and whose cell of origin is unknown. ASPS arises mainly in children and young adults and can migrate into other parts of the body, typically the lungs and the brain. ASPS is a sarcoma, and that indicates that this cancer initially arises from tissue of embryonic mesenchymal origin. Typically, ASPS arises in muscles and deep soft tissue of the thigh or the leg, but can also appear in the upper extremities. While ASPS is a soft tissue sarcoma, it can also spread and grow inside the bones.
The term alveolar comes from the microscopic pattern, visible during the analysis of slides of ASPS under the microscope in histopathology. The tumor cells seem to be arranged in the same pattern as the cells of the small air sacks in the lungs. However, this is just a structural similarity. ASPS was first described and characterized in 1952.
ASPS may exist in the patient’s body for a long time before being diagnosed. It can grow large and push aside surrounding tissues for a long time before causing any discomfort. Therefore, ASPS symptoms may either be a painless swelling, or a soreness caused by compressed nerves or muscles, affecting the range of motion in the area.
Pathology
The definitive diagnosis of ASPS is based on its appearance under the microscope, i.e. its histomorphology, and presence of the characteristic chromosomal translocation. ASPS' histomorphologic features include an alveolar-like pattern at low magnification and the presence of large cells with abundant eosinophilic cytoplasm and eccentric nuclei. Calcifications are commonly present, as may be seen with slow growing neoplasms.
Prognosis
Although ASPS displays a relatively indolent course, the ultimate prognosis is poor and is often characterized by late metastases.
Epidemiology
ASPS is an extremely rare cancer. While sarcomas comprise about 1% of all newly diagnosed cancers, and 15% of all childhood cancers, ASPS comprises less than 1% of sarcomas. According to the American Cancer Society, about 9530 new cases of soft tissue sarcoma will be diagnosed in the USA in 2006. This predicts under 100 new cases of ASPS. Such low numbers of occurrence seriously impede the search for a cure by making it hard to gather any meaningful statistics about the disease. As a result, finding the best treatment option often involves making a lot of educated guesses.
Researchers at the Huntsman Cancer Institute in Utah demonstrated that ASPS might be driven in part by lactate both being used as a fuel and driving angiogenesis.
In terms of origin, it was recently demonstrated that although ASPS generally arises in muscle tissue, the cells do not express muscle markers at the mRNA level and more closely resemble mesenchymal stromal cells.
