Synovial osteochondromatosis

A malignant sarcoma of soft tissue that arises near but not in a joint, most often in an adolescent or young adult, is typically slow-growing, and may escapes notice until it causes pain.

These tumors occur mainly in the arms or legs in the area of large joints, especially the knees.

Less frequently, the disease develops in the head and neck or in the trunk.

While the tumor is called synovial sarcoma (or synoviosarcoma), it has never been shown to arise from synovial cells (the cells that line a joint).

The cell of origin is not known.

The diagnosis of this tumor can be suspected by X-ray or imaging, made by biopsy, and confirmed by chromosome studies.

Cytogenetic studies reveal a translocation (an exchange of material) between the X chromosome and chromosome 18, termed t(X;18)(p11.2;q11.2), in the tumor cells.

This translocation is present in virtually all cases of synovial sarcoma and is specific to this tumor.

The translocation creates a chimeric (fusion) gene by making new neighbors of the SYT gene from chromosome 18 and one of two highly homologous (almost identical) genes SSX1 or SSX2 on the X chromosome.

The most common treatment for the tumor is surgery to remove the entire tumor, nearby muscle, and lymph nodes.

Some patients have radiation, chemotherapy, or a combination of treatment methods.

Synovial sarcoma tends to recur locally and to involve regional lymph nodes.

Distant metastasis (spread) occurs in half of cases, sometimes many years after the initial diagnosis.