Alveolar Soft Part Sarcoma (ASPS) is a very rare, slow growing tumor from an unknown origin that arises mainly in children and young adults. ASPS is highly angiogenic: it involves intensive growth of new blood vessels, that connect the tumor to the blood system and enable dissemination of tumor cells into the blood stream. Those tumor cells can then easily migrate into other parts of the body typically lungs and brain.

ASPS is a sarcoma and that indicates that this cancer initially arises in tissues that connect, support, or surround other structures and organs of the body. The term “soft tissue” indicates that this sarcoma does not originate in bone, but in soft connective tissues. ASPS arises in muscles and deep soft tissue of the thigh or leg (low extremities), but many times will appear in the upper extremities: hands, the neck and head. While ASPS is soft tissue sarcoma, it may spread and grow inside bones.

The term “Alveolar” in the name Alveolar Soft Part Sarcoma (ASPS) comes from the microscopic pattern (histopathology) that one sees upon analysis of slides of ASPS under the microscope: the cells of the tumor seem to be arranged in the same pattern that cells of the small air sacks (alveoli) are organized in the lung. However, this is just a structural similarity. ASPS was first described and characterized in 1952 by a pathologist named Christopherson.

ASPS is a rare cancer. While sarcomas are making about 1% of all the cancers and 15% of all childhood cancers, ASPS is only less than1% of all the sarcoma cases. According to the American Cancer Society, about 9530 new cases of soft tissue sarcoma will be diagnosed in the USA in 2006 and that predicts about 95 new cases of ASPS.

ASPS may exist in the patient’s body for a long time before being diagnosed. It can grow large and push aside surrounding tissues long before causing 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 affected area.

What causes ASPS

Chromosomal analysis of ASPS shows breaking and joining of two chromosomes (chromosomal translocation) in the tumor cells. A piece of chromosome X breaks and is joined to chromosome 17. This translocation creates a fusion between two genes named ASPL and TFE3 (ASPL-TFE3 fusion transcript), which results in the formation of an aberrant protein (termed fusion protein). This fusion protein is not found in normal cells. Two forms of ASPL-TFE3 fusion proteins are detected in ASPS patients, defining two ASPS types: Type 1 and type 2. Currently it is not known if the prognosis of ASPS patients with type I is different from those with type II ASPS.

Dr. Ladanyi, at the Memorial Sloan-Kettering Cancer Center, in New York, has pioneered this work.