Related narrative: Sarcoma of the Knee
Malignant neoplasms are categorized broadly according to their tissue of origin: a.) those derived from one parenchymal cell type; b.) those derived from one germ cell layer, but which contain more than one neoplastic cell type [i.e., mixed tumors]; and c.) those derived from more than one germ cell layer, and which contain more than one neoplastic cell type [i.e., teratogenous]. The malignant neoplasms derived from one parenchymal cell type are further divided into those of mesenchymal origin, termed sarcomas and those of epithelial origin, termed carcinomas.
Determining the histogenesis of a particular sarcoma is often an arduous task both clinically and microscopically, but such efforts are always essential. Doing so can provide a wealth of information concerning tumor behavior, allowing all medical specialists involved to develop a more effective treatment plan for the patient. The association of various sarcomas with specific chromosomal abnormalities (translocations, mutations, deletions and additions) also has enormous diagnostic potential and perhaps even predictive value (1). Such cytogenetic studies could actually help to specify a sarcoma previously diagnosed as "not otherwise specified".
One technique often used is polymerase chain reaction (PCR). PCR requires repetition of three reactions: a.) denaturation of double-stranded DNA; b.) annealing of a single-stranded DNA template with primers which are complementary to to regions flanking the DNA segment to be replicated; and c.) extension of the DNA segments with the addition of nucleotides, resulting in two identical copies of the DNA segment. If the DNA segment to be replicated is particularly long, RNA must first be converted to DNA before PCR is begun. This process is called reverse transcriptase polymerase chain reaction (RT-PCR).
Another method of determining histogenesis is through immunohistochemistry. This is perhaps the most widely used method in pathology laboratories, primarily because of its ease of performance, as well as ease of interpretation. Immunohistochemical (IHC) stains are applied to cut sections of paraffin-embedded tissue on glass slides. They "highlight" identifiable marker proteins for various soft tissue phenotypes, thus enabling histogenic differentiation (2).
Synovial sarcoma is a malignant mesenchymal neoplasm that primarily affects adolescents and young adults. The most common sites of occurrence are the paraarticular regions of the extremities; however, head & neck and abdominal lesions can also occur (3). A deep, painful, slow-growing swelling is the usual initial presentation, and may follow a traumatic injury to that site (4). Radiographic findings of synovial sarcoma show masses of moderate density and multifocal calcifications in close proximity to a joint capsule. CT scans and MRI's are methods of determining exact location of these lesions, however, most radiologist find plain film radiographs more valuable in providing an initial diagnosis.
Microscopically, four types of synovial sarcomas are recognized: a.) biphasic type, containing both epithelial and spindle cells; b.) monophasic fibrous type, primarily spindle cells; c.) monophasic epithelial type; and d.) poorly differentiated type. By far, the most common type is the biphasic type, which features cuboidal to columnar epithelial strands surrounded by lighter staining spindle cells. These sarcomas positively coexpress cytokeratin and epithelial membrane antigen (EMA) on immunohistochemical stains. These stains are very useful in differentiating synovial sarcoma from fibrosarcoma. Poorly differentiated types of synovial sarcoma are more of a diagnostic challenge than the other types. However, some features that can be helpful are, pseudorosettes in an epitheliod background.
True rosettes (Flexner-Wintersteiner rosettes) are not usually found in synovial sarcomas, and are more characteristic of primitive neuroectodermal tumors (PNET). PNET's have been associated with translocations of chromosomes 11 and 22, t(11,22). When true rosettes are found within a synovial sarcoma (very rare), molecular evaluation for EWS/FLI-1 gene fusion products associated with t(11,22) is useful in determining if a second malignant biological process is concomitantly occuring, or if this is merely a rare variation of synovial sarcoma. Synovial sarcomas have been associated with a translocation between chromosomes X and 18, t(X,18). The ten-year survival rate for synovial sarcomas in general ranges from 20% to 63% (5).
1. Fletcher CDM, Akerman M, et al. Correlation between clinicopathological features and karyotype in lipomatous tumors Ō a report of 178 cases from the chromosomes and morphology collaborative study group. Am J Pathol 1996;148:623-30.
2. Brooks JS. Immunohistochemistry in the differential diagnosis of soft tissue tumors. Monogr Pathol 1996;38:65-128.
3. Weiss SW, Goldblum JR. Enzinger and WeissĖs Soft Tissue Tumors. Mosby. 2001;1483-1509.
4. Vincent RG: Malignant synovioma. Ann Surg 1960;152:777.
5. Weiss SW, Goldblum JR. Enzinger and WeissĖs Soft Tissue Tumors. Mosby. 2001;1483-1509.