These tumors arise around the joints (not within the joint space) close to bursae, joint capsule and tendon sheath, in the abdominal wall, in the pharyngeal region and less frequently at other sites.
The synovial sarcoma exhibits a range of biologic behavior ranging from an indolent tumor with a long survival to tumors that lead to death within a few months.
In most tumors, reciprocal translocation between chromosome 18 and X is seen.
Most tumors occur between the ages of 15-35 and the male to female ratio is 1.5:1.
These tumors often (60%) arise in the lower extremities around the knees, ankles and feet. In 25% of cases, these tumors are found in the upper extremities between the shoulders and elbows.
These tumors may measure from a few cm to large masses. The small lesions exhibit a well defined border, an apparent capsule, and are round to multilobular and firm. The cut surface exhibits a gray-white appearance. Cystic spaces may be present. Large lesions gain a sarcomatous appearance and show areas of hemorrhage, necrosis, cysts, and calcifications.
Microscopically, these tumors are commonly biphasic and consist of a spindle cell component and epithelial cells forming glandular and papillary structures. Some tumors are monophasic and consist either of the spindle cells or the epithelial cells. The epithelial cells are arranges as glands, microcystic structures and in some areas merge imperceptibly with the spindle cell component. These epithelial cells have abundant cytoplasm, large nuclei and do not exhibit marked variability in size. The spindle cell stroma consists of fibroblast-like cells that exhibit more variability in terms of their size and nuclear features. Giant cells and mitotic figures are not frequent. Additional diagnostic features include presence of diastase resistant PAS positive secretions within the epithelial cells, focal calcifications within the spindle cell component and psedoglandular cystic spaces. Immunohistochemical staining reveals presence of cytokeratin both in the epithelial and spindle cell component. At the ultrastructural level, irregular microvilli are present on the epithelial cells facing the lumen.