Alveolar Soft Part Sarcoma (ASPS) is a soft tissue tumor.  The term sarcoma refers to malignant tumors of tissues that connect, support, or surround other structures and organs of the body such as bone, cartilage, fat, muscle.  Sarcomas are making about 1% of all cancer types and 15% of all childhood cancers.  The term Soft Tissue indicates that ASPS is not a bone cancer, but is related to cancers that includes muscles, tendons, fibrous tissues, fat, blood vessels, nerves, and synovial tissues (tissues around joints).  According to the American Cancer Society, about 8680 new cases of soft tissue sarcoma will be diagnosed in the US in 2004 and up to 1% of those cases will be ASPS.

The name Alveolar Soft Part Sarcoma (ASPS) is derived from the histopathology of this cancer (microscopic pattern).  ASPS was first described and characterized in 1952 by a pathologist named Christopherson.  Most ASPS cases occur in patients during their second and third decade of life with a slight female predilection.  Most commonly, it involves the muscles and deep soft tissue of the pelvis and the extremities.  ASPS is a slow growing tumor and is highly vascular (rich in blood vessels).

ASPS tumor may exist 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. ASPS can metastasize (spread and invade) into other organs of the body.  The metastatic tumors (mets) are similar to those of the primary (original) ASPS tumor.  The most common organs where ASPS metastasize into them are lungs and brain. 

Chromosomal analysis of ASPS cells shows breaking and joining of two chromosomes (chromosomal rearrangement).  This rearrangement is termed translocation and involves the break of a piece from chromosome X and its fusion to chromosome 17.  The translocation creates an abnormal fusion between two genes named ASPL and TFE3.  This results in the formation of an aberrant protein (termed fusion protein) that is not found in normal cells.  Two kinds of fusions were identified in ASPS between these two genes.  Therefore there are two types of ASPS: type 1 and type 2.  This work has been pioneered by Dr. Ladanyi, at the Memorial Sloan-Kettering Cancer Center, in New York.