Alveolar soft part sarcoma (ASPS) is a rare sarcoma (malignant tumor of connective tissue) of an unclear cause. It is among the least common sarcomas, representing 0.2-1 percent of large studies of soft tissue sarcomas. Since there are approximately 8000 soft-tissue sarcomas per year that arise in the United States, this means there are on the order of 15 to 80 cases nationwide each year. It is characterized by a painless mass in the leg or buttock, with a particular affinity to travel to the lungs as multiple nodules, presumably while the sarcoma itself is still small. ASPS is very rare, because it involves a specific breaking and joining event between two chromosomes, called an "unbalanced translocation". This finding is observed in essentially all ASPS examined so far. This finding cannot be passed on to children, however, as the finding occurs only in the tumor, not in the normal cells; in addition, there are no families in which multiple family members have ASPS. [ Back ]