Head and neck synovial cell sarcoma

Synovial sarcoma of the larynx in a 79-year-old woman, confirmed by karyotyping and fluorescence in situ hybridization analysis

BACKGROUND

Synovial sarcoma is an uncommon tumor of the head and neck and is an exceedingly rare finding in the larynx. Generally, it afflicts younger patients and most often occurs in the hypopharynx.

METHODS AND RESULTS

We report a case of a biphasic synovial sarcoma arising in the arytenoid fold of a 79-year-old woman. The diagnosis was confirmed by an extensive immunohistochemical panel, karyotyping, and fluorescence in situ hybridization (FISH). The patient was treated with total laryngectomy, and she did well postoperatively.

CONCLUSION

To our knowledge, our patient is the oldest ever to be reported in the literature, concluding that although this entity is considered a disease of young patients, it still has to be included in the differential diagnosis in older patients. Second, our report is only the third to describe t(X;18) (p11.2;q11.2) by karyotyping and the first ever by using FISH analysis, thus adding more cytogenetic data to the literature in this rare location and confirming the use of FISH in making the accurate diagnosis.

Survival in patients with synovial sarcoma of the head and neck: Association with tumor location, size, and extension

BACKGROUND

The medical literature on synovial sarcoma (SS) of the head and neck region is limited. Thus, we determined whether clinical characteristics and treatment were associated with recurrence and survival rates in patients with SS of the head and neck.

METHODS

We retrospectively identified patients with a pathologic diagnosis of SS of the head and neck at our institution (a large tertiary comprehensive cancer center) and compared recurrence and survival rates by clinical characteristics and treatment.

RESULTS

Forty patients with SS of the head and neck were identified from 1945 to 2004 (first case in 1968), representing <5% of all head and neck sarcomas seen at our institution during this time period. Twenty-three patients (58%) had the monophasic histologic subtype, 15 (38%) biphasic, and 2 unspecified. Most patients were male (73%), with a median age of 29 years. SS tumors were most commonly located in the neck (60%); thus, the most common symptoms were a neck mass and neck pain. No patients reported a history of radiation exposure. Higher disease-specific and overall survival rates were associated with upper aerodigestive tract location, tumors of < or =5 cm, and tumors did not extend into bone. Patients treated with surgery and adjuvant radiotherapy had higher survival and lower recurrence rates than did those treated with surgery alone or a combination of surgery, radiotherapy, and chemotherapy. This difference was not significant, and the subgroups were small, with substantial confounding by adverse prognostic factors.

CONCLUSIONS

SS of the head and neck is extremely rare, and our results should be viewed with caution given the relatively small group size and treatment over a 36-year period. Survival rates were associated with tumor location, size, and extension. Treatment of SS of the head and neck should be directed toward complete surgical resection. Given the known sensitivity of SS to contemporary chemotherapy, a multimodality approach should be considered in the perioperative setting, especially in high risk patients.

Biphasic Synovial Sarcoma of the Posterior Pharyngeal Wall: A Case Report

Synovial sarcoma is not common in the head and neck region. Because its histopathologic features are many and varied, it is often misdiagnosed. We report a case of biphasic synovial sarcoma of the posterior pharyngeal wall, and we discuss the clinical and pathologic features of this case.

Primary Intrathoracic Synovial Sarcoma

Synovial sarcoma (SS), an aggressive neoplasm accounting for up to 14% of soft tissue sarcomas, was recently recognized as a primary tumor in the lung and pleura. SS is characterized by the chromosomal translocation t(X;18)(SYT-SSX) found in more than 95% of the tumors. We report a cooperative study from the French Sarcoma Group and the Mesopath Group on 40 t(X;18)(SYT-SSX)-positive primary intrathoracic SS. There were 22 males and 18 females, whose age ranged from 16 to 79 years (median, 47 years). Neoplasms were mostly circumscribed and of large size (median, 7.5 cm; range, 2-16 cm). Thirty-nine tumors were monophasic SS, including 24 (60%) monophasic fibrous and 15 (37.5%) poorly differentiated cases, and one lesion was a biphasic SS. A larger proportion of poorly differentiated tumors were observed among intrathoracic SS as compared with soft tissue SS. Immunohistochemically, 90% of the cases reacted with at least one epithelial marker. CD34 was focally expressed in 3 cases. SYT-SSX1 fusion transcripts were detected in 22 cases (56.4%) and SYT-SSX2 fusion transcripts in 17 cases. Median and 5-year disease-specific survival in 33 patients was 50 months and 31.6%. Median and 5-year disease-free survival was 24 months and 20.9%. Patient sex, age, tumor size, histologic subtype, grade, and SYS-SSX fusion type had no significant impact on outcome. In conclusion, intrathoracic SS are rare but aggressive tumors with poor prognosis. In this unusual location, the detection of SYT-SSX fusion transcripts is a valuable diagnostic adjunct.

Primary synovial sarcoma of the parotid gland

Synovial sarcoma typically develops in the deep soft tissues of the extremities in adolescents and young adults. Uncommonly, these tumors may arise (9%) in the head and neck region (9%), especially at the cervical and parapharyngeal sites. Primary synovial sarcoma of the parotid gland is a rare occurrence that may not uncommonly cause differential diagnostic difficulties. In these cases, an origin from within the gland rather than a secondary involvement by tumor from a surrounding structure must be confirmed. We report a new case of biphasic synovial sarcoma arising in the parotid gland and review the previously documented cases.

C-erb-B2 (HER2/neu) expression in synovial sarcoma of the head and neck

BACKGROUND

Synovial sarcoma is a malignant mesenchymal tumor composed of varying proportions of spindle and epithelial cell components. Because of the histologic and immunohistochemical similarity of synovial sarcoma to epithelial carcinomas, we hypothesized that the human epithelial growth factor receptor 2 (C-erb-B2, also termed HER2/neu) may contribute to the tumor phenotype and provide a new therapeutic target for this soft tissue tumor.

METHODS

Three head and neck, one chest wall, and seven extremity synovial sarcomas were evaluated for C-erb-B2 (HER2/neu) expression by immunohistochemistry, Western immunoblotting, and fluorescence in situ hybridization (FISH).

RESULTS

The head and neck cases demonstrated immunohistochemically strong positive staining, whereas tumors from other anatomic locations showed neither positive nor cytoplasmic restricted staining. Antigen-targeted antibody therapy (trastuzumab) was initiated in two patients.

CONCLUSIONS

These results demonstrate that C-erb-B2 (HER2/neu) may play a role in the tumorigenesis of synovial sarcoma; and, therefore, antigrowth factor therapies may provide a previously unrecognized pharmaceutical approach to soft tissue tumors. The data also suggest that although synovial sarcoma of the head and neck and synovial sarcoma of the extremities have similar morphologic features, they may be clinically and mechanistically distinct entities.

Intra-abdominal synovial sarcoma: a clinicopathological study

AIMS

To evaluate a series of synovial sarcomas arising in the abdomen, pelvic cavity, or retroperitoneum. Synovial sarcoma is rare within the abdomen. In this location, it can be confused with other biphasic tumours and with other spindle and round cell sarcomas.

METHODS AND RESULTS

Cases were retrieved from archives. There were 11 intra-abdominal tumours among 300 synovial sarcomas in two referral practices (3.7%). Three were pelvic (two midline, one sidewall) and eight were retroperitoneal. They occurred in six males and five females aged from 25 to 75 years (mean 49 years, median 46 years), and ranged in diameter from 65 to 470 mm (mean 210 mm, median 150 mm). Six examples were biphasic, five were monophasic and seven had poorly differentiated areas. Monophasic tumours displayed at least one epithelial marker. One biphasic tumour had a SYT-SSX2 fusion gene. Seven sarcomas were high-grade and four of intermediate grade malignancy. Follow-up data were available in 10 patients. In all but one case, tumour recurred or metastasized within the abdomen. The pelvic sarcomas also metastasized outside the abdomen. Eight of 10 patients (80%) died of disease with survival from 4 to 36 months (mean 17 months, median 18 months). Two patients were alive with disease at 43 and 48 months.

CONCLUSIONS

Synovial sarcomas rarely arise within the abdomen and pelvis. They occur mainly in middle age, attain a large size, are difficult to excise and recur locally. Pelvic tumours metastasize distantly. Retroperitoneal tumours remain confined to the abdomen and, unlike synovial sarcomas elsewhere, do not metastasize remotely, although mortality is high.

Pulmonary synovial sarcoma with polypoid endobronchial growth: A case report, immunohistochemical and cytogenetic study*

A rare case of primary pulmonary synovial sarcoma with polypoid endobronchial growth in a 42-year-old Japanese woman is described. Left upper sleeve lobectomy was performed for the polypoid tumor measuring 2.5 cm in the left major bronchus and the patient was treated with adjuvant chemotherapy. Three years later, a recurrent tumor was discovered. Microscopically, this tumor was characterized by a proliferation of oval to spindle-shaped cells arranged in sheets and fascicles and covered by the thin normal bronchial epithelium. Immunohistochemically, tumor cells were positive for vimentin, and focally positive for pancytokeratin recognized by AE1/AE3, cytokeratin 7 and epithelial membrane antigen. A chimera gene, SYT-SSX1, was detected. Recently, primary pulmonary synovial sarcoma is an increasingly recognized clinical entity; however, most of these tumors present as a parenchymal mass. The present case is a unique example of primary synovial sarcoma of endobronchial polypoid type. This case suggests that pulmonary synovial sarcoma might originate from bronchial submucosal stromal tissue.

Oral synovial sarcoma: a report of 2 cases and a review of the literature

The head and neck region constitutes the second most common site of involvement for synovial sarcoma, accounting for up to 10% of all cases. Intraoral synovial sarcoma is rare; in fact, only 29 cases have been reported. We describe 2 additional cases occurring in the floor of the mouth and the retromolar area. In addition, we have reviewed the clinicopathologic features of the previously reported cases. Our findings indicate that intraoral lesions differ from lesions occurring in other sites only in that intraoral cases show a greater male predilection and a generally painless initial presentation. In the oral cavity, the possible earlier detection, easy accessibility, and small size render these tumors more likely to be amenable to surgical excision, but their biologic behavior remains aggressive, with a poor long-term prognosis. Awareness of the potential for the occurrence of this neoplasm in the oral cavity is important for effective histopathologic diagnosis of intraoral spindle cell malignancies.

Sarcomas of the head and neck region

PURPOSE OF REVIEW

This review discusses the classification, etiology, diagnosis, evaluation, treatment, and prognosis of sarcoma of the head and neck region.

RECENT FINDINGS

Sarcomas account for less than 1% of all malignancies in the United States with only 5 to 15% of these sarcomas occurring in the head and neck region. However, about 1 in 3 pediatric sarcomas will occur in the head and neck region. Occasionally, these tumors are associated with genetic syndromes or previous radiation exposures, but, most commonly, no clear etiology exists. Pathologic classification is critical to the ultimate treatment and prognosis of sarcoma of the head and neck. Osteosarcoma, rhabdomyosarcoma, malignant fibrous histiocytoma, and angiosarcoma are the most common types of sarcoma to occur in the head and neck region; however, up to 20% of head and neck sarcomas will remain unclassified. Surgery has been central to the management of these malignancies with some exceptions in the pediatric population. Adjuvant chemotherapy is being utilized and/or studied for most high-grade sarcomas and adjuvant radiotherapy is important for disease control in high-grade soft-tissue sarcomas. Prognosis is clearly related to tumor grade and margin status.

SUMMARY

Sarcomas of the head and neck region are rare malignancies often without a clear etiology. Expert pathologic review and classification is critical, as are quality imaging and multidisciplinary management.

Sarcomas of the head and neck

With the exception of pediatric RMS, soft tissue sarcomas only rarely arise in the head and neck region. Soft tissue sarcomas include a diverse array of histologic types because of the variety of mesenchymal tissues from which they originate. The combination of infrequent occurrence, varied pathologic features, and the many potential sites of presentation makes these tumors a challenge for the head and neck oncologist and underscore the need for review by a pathologist experienced with soft tissue tumors. Classification schemes that group sarcomas according to grade have been helpful in providing prognostic information. Although local control of the primary tumor is critical to successful treatment of both high- and low-grade lesions, the high rate of distant metastases in high-grade tumors supports the role of combined modality therapy. Compared with other types of head and neck neoplasms, such as squamous cell carcinoma, soft tissue sarcomas have low rates of regional metastases. Surgery generally has been recommended as the primary method of treatment for achieving local control, except in those high-grade tumors arising in sites not amenable to resection. Exceptions to this principle include RMSs of the orbit, paranasal sinuses, and masticator space in children; these are usually treated with radiotherapy and combined multiagent chemotherapy, thereby avoiding the functional and cosmetic impact of surgery. Also, extensive angiosarcomas of the scalp should be treated with multimodality therapy combining surgery and wide-field radiation therapy in an attempt to achieve local control. Adjuvant radiotherapy is generally recommended for high-grade sarcomas, large tumors, close or positive surgical margins, and certain histologic variants. Systemic chemotherapy is recommended for those tumors with a significant risk of distant metastases. Increasingly, neoadjuvant chemotherapy is being used to determine responsiveness to chemotherapy, which can help physicians select patients who may benefit from systemic postoperative therapy. Traditional predictors of treatment failure for soft tissue sarcomas include larger tumor size, high-grade histology, and positive surgical margins. The advent of more advanced reconstructive techniques, including free tissue transfer, has made more aggressive surgical resection of these tumors possible. Nevertheless, a considerable number of ancillary support staff are critical to the patient's postoperative rehabilitation and eventual return to a satisfactory level of function and quality of life. In the future, the discovery of the molecular pathogenesis of specific tumor types, such as the cytogenetic findings in synovial sarcoma, will improve physicians' prognostic abilities and selection of patients who are most likely to benefit from emerging adjuvant therapies.

A synovial sarcoma beneath the pectoralis major muscle

Synovial sarcoma is a rare malignant neoplasm that develops most frequently in the extremities. A 68-year-old man presented with a painful mass on the right side of his chest with a 10-year history. Gross findings revealed a mass beneath the pectoralis major muscle. The pathologic findings showed the tumor was predominantly composed of spindle cells the arranged in compact interdigitating fascicles and scattered epithelial nests were seen. A diagnosis of synovial sarcoma was made.

Submandibular synovial sarcoma with t(X;18) and synovial sarcoma of the toe with additional cytogenetic abnormalities: presentation of two cases and review of the literature

We report cytogenetic findings from fine-needle aspiration samples of two synovial sarcoma patients. The cases are of interest because (1) one case is of a rare site (submandibular region) of the head and neck, and (2) the other is a patient with synovial sarcoma of the toe showing additional cytogenetic abnormalities along with t(X;18). The literature of this tumor is reviewed.

Monophasic synovial sarcoma of the neck in an 8-year-old girl resembling a thyroglossal duct cyst

Synovial sarcomas of the head and neck are rare. Typically, they are localized laterally in the parapharyngeal space. We report the case of an 8-year-old girl with a monophasic round cell synovial sarcoma of the anterior neck, clinically resembling a thyroglossal duct cyst. Histologic, immunohistochemic and cytogenetic findings are presented with a brief review of the literature. This case reaffirms the importance of considering malignant neoplasms in the differential diagnosis of pediatric neck masses.

Primary pleuropulmonary synovial sarcoma: reappraisal of a recently described anatomic subset

BACKGROUND

Primary pleuropulmonary synovial sarcoma (SS) is a rare neoplasm and a recently recognized anatomic subset. Its clinicopathologic attributes are not yet well defined.

METHODS

In this study, the clinical and histopathologic features of 12 SS arising in the lung and/or pleura were analyzed.

RESULTS

The neoplasms occurred in 7 men and 5 women, 20-72 years old (median, 31 years), were well circumscribed with a mean size of 7.2 cm, and involved either lung (9 cases), pleura (2 cases), or both (1 case). All the tumors were of monophasic type. Nine showed a classic spindle cell pattern, and three showed predominantly poorly differentiated features. All but one case showed at least focal positivity for epithelial membrane antigen (EMA), a finding characteristic of this tumor. The lack of EMA staining in one case, proven by electron microscopy to be SS, was attributed to the scarcity of material available for immunohistochemical stains. The diagnosis was proven cytogenetically in three cases. Within 2 years, local recurrence developed in 8 patients (75%), 3 of whom developed metastasis (25%). Five patients died of their disease within 2.5 years, 4 of them from uncontrolled local disease.

CONCLUSIONS

The authors conclude that pleuropulmonary SS, although rare, represents a distinct anatomic subset having pathologic features similar to those of its soft tissue counterpart. Its clinical behavior appears more aggressive, perhaps because of relatively later presentation combined with the difficulty in obtaining a wide surgical margin.

Small-cell variant of synovial sarcoma: fine-needle aspiration with ancillary features and potential diagnostic pitfalls

We report a small-cell variant of synovial sarcoma examined by fine-needle aspiration (FNA) biopsy. The patient is a 23-yr-old female who had a synovial sarcoma involving the left infratemporal region, diagnosed at 7 yr of age, followed by a metastatic lesion involving the lung and chest wall 16 yr later. The chest wall metastases was sampled by FNA biopsy. The aspirate consisted of numerous, small, round cells with very high nuclear-to-cytoplasmic ratios. The cytomorphologic features could potentially be confused with other pediatric small round cell tumors. Ancillary studies demonstrated positive staining of the neoplastic cells for cytokeratin, epithelial membrane antigen (EMA), and CD99. The differential diagnosis of other small round cell tumors that may be mistaken for the small-cell variant of synovial sarcoma are presented. We believe that this is the first FNA report detailing the cytologic and ancillary features of the small-cell variant of synovial sarcoma.

Management of the clinically negative cervical lymph nodes in patients with non-conventional squamous carcinoma of the larynx

This paper discusses the indications for neck dissection in those patients with laryngeal tumours which prove to be, on pathologic examination, not conventional squamous carcinomas but rather fall into the category either of one of the uncommon histological subtypes of carcinoma, or another type of unusual histological variant of laryngeal malignancy, a mesenchymal tumour. It appears as though these unusual laryngeal malignancies may manifest both biological behaviours and propensities to metastasize to regional lymph nodes that differ from those of the more commonly encountered conventional squamous carcinomas of the larynx. This heterogeneous group of tumours accounts for about 10 per cent of all malignant tumours of the larynx.

Synovial sarcoma in the parapharyngeal space: case report and review of the literature

We encountered a rare case of synovial sarcoma in the parapharynx of a 47-year-old Japanese man. This patient presented with an enlarging tumor in the right side of his neck that had grown progressively over a 4-week period. Radiological examinations revealed that the tumor arose from the parapharyngeal space. The tumor could not be completely removed at surgery. Metastasis to the lumbar vertebra was detected postoperatively. The patient underwent three courses of chemotherapy and the delivery of palliative radiation to the lumbar vertebra without success. The patient died of lung metastasis 7 months after surgery.

Synovial sarcoma

Synovial sarcoma is a rare soft tissue tumor of children and adults that is unrelated to synovium and can occur in almost any part of the body. The familiar biphasic synovial sarcoma has discernible glandular or solid epithelial structures, and monophasic forms have characteristic ovoid or spindle cells with only immunohistochemical or ultrastructural evidence of epithelial differentiation. There are several morphologic patterns, including myxoid and hemangiopericytic, and behaviorally distinct calcifying, ossifying, and poorly differentiated subtypes can be recognized. Most synovial sarcomas are immunoreactive for cytokeratin, epithelial membrane antigen, and bc12 protein, and negative for CD34, and many express S100 protein and CD99 (MIC2). Nearly all synovial sarcomas have a specific t(x;18) (p11.2;q11.2) chromosomal abnormality, resulting in fusion of either of two variants of the SSX gene with the SYT gene; the genetic features may relate to morphology and outcome. The differential diagnosis can include a wide range of spindled, polygonal, or round cell sarcomas. Clinically, there have been marked recent improvements in local control of disease and lesser ones in management of metastases. The pathology, differential diagnosis, and behavior of this unique tumor are reviewed.

Primary cutaneous synovial sarcoma: a case report

We present a case of synovial sarcoma involving the cutaneous tissue of the knee in an 18-year-old woman. The 2.5 cm tumor was locally excised and recurred six times over the following 24 years. The neoplasm involved the deep dermis with extension into the papillary dermis and superficial subcutis. The tumor was predominantly composed of spindle cells arranged in compact interdigitating fascicles and scattered epithelial nests were seen. Focal myxoid and hemangiopericytoma-like areas as well as numerous mast cells were identified. Spindle cells stained for vimentin, CAM 5.2, and epithelial membrane antigen, whereas epithelial nests only stained for CAM 5.2 and epithelial membrane antigen. Neither component was reactive for antibodies directed against desmin, muscle specific actin, smooth muscle actin, S-100 protein, CD-31, or CD-34. This newly reported location for this morphologically heterogeneous tumor creates potential diagnostic confusion with other primary neoplasms in these areas.

Synovial sarcoma of the larynx

A 23 years old male presented with a soft cystic mass in the left paralaryngeal space since 3 months. Indirect laryngoscopy revealed a bulging of the left lateral pharyngeal wall. Histopathologic al examination of the biopsy proved it to be a synovial sarcoma. The case is the seventh case reported in literature.

Regional and distant metastases in laryngeal and hypopharyngeal sarcomas

Cervical node and distant metastases are the most important prognostic factors in malignant laryngeal neoplasms. Owing to the unusual occurrence of laryngeal sarcomas, the prevalence of their metastases has never been analyzed in detail. We reviewed the laryngeal sarcomas reported in the literature and noticed that both regional and distant metastases are rare events and variable for different histotypes. These observations have obvious therapeutic and prognostic implications.

Synovial sarcoma of the head and neck: chromosomal translation (X;18) as a diagnostic aid

BACKGROUND

Synovial sarcoma, a rare tumor in the head and neck, has been historically diagnosed by its characteristic biphasic histologic pattern. Monophasic variants exist which can be difficult to diagnose.

METHODS

Two cases of synovial sarcoma of the head and neck are presented. Both cases, cytogenetic analysis was performed using standard protocols.

RESULTS

Both tumors demonstrated a chromosomal translocation, t(X;18)(p11.2;q11.2), which either made or confirmed the diagnosis.

CONCLUSIONS

Synovial sarcoma contains a characteristic chromosomal translocation which is a useful diagnostic tool, especially when histologic studies are equivocal.

Laryngeal chondrosarcomas: the Mayo Clinic experience

BACKGROUND

Laryngeal chondrosarcomas occur infrequently. Their management is often guided by inferences made from the management of sarcomas arising from more commonly afflicted organs.

METHOD

A retrospective analysis of patients with laryngeal chondrosarcomas treated at the Mayo Clinic between 1959 and 1992 was performed to assess prognostic factors and outcomes after various treatments.

RESULTS

A total of 20 patients received treatment during this time period. All chondrosarcomas were low grade; 19 involved the cricoid cartilage and one arose in the supraglottic larynx. Initial treatment consisted of local excision (often subtotal removal) alone in 12 patients (60%), hemilaryngectomy in 2 (10%), near total laryngectomy in 2 (10%), and total laryngectomy in 4 (20%). Six patients (30%) had local recurrence: five initially had local excision and one had hemilaryngectomy. All local recurrences or tumor progression developed >3 years after initial treatment. Salvage surgery was performed in five of the six patients who had local recurrence, and the other patient was observed. Of the five patients who had salvage surgery, three required another resection because of a second recurrence.

CONCLUSIONS

These results suggest that initial conservative subtotal laryngectomy should be explored further because this treatment may provide long-term voice preservation in most patients, and patients who experience a recurrence after local excision often have been given several years of voice preservation.

Primary pulmonary sarcomas with features of monophasic synovial sarcoma: a clinicopathological, immunohistochemical, and ultrastructural study of 25 cases

We present 25 cases of a primary pulmonary sarcoma bearing histological, immunohistochemical, and ultrastructural features indistinguishable from those of monophasic synovial sarcoma of soft tissue. The patients were 11 men and 14 women between the ages of 16 and 77 years. Clinically, the most common symptoms were chest pain, cough, shortness of breath, and hemoptysis. The lesions involved all lung segments. Grossly, they varied in size from 0.6 to 20 cm and were described as soft to rubbery tumors with areas of necrosis and hemorrhage, some with cystic changes. Two lesions involved the bronchial wall and in one case the tumor was described as encircling the bronchial tree. Histologically, all of the lesions were characterized by an atypical spindle cell proliferation with a solid growth pattern. Areas of myxoid, neural, hemangiopericytic, and epithelial-like growth pattern were observed. Mitoses, necrosis, and hemorrhage were seen in all lesions in varying proportions. Immunohistochemical studies for epithelial membrane antigen (EMA) and keratin showed strong focal positivity in 25 of 25 and 23 of 25 lesions, respectively. Immunohistochemical study for vimentin showed diffuse strong positivity in all lesions. Other immunostains, including desmin, smooth muscle actin, and S-100 protein, were negative. Electron microscopy in three cases showed spindle cells with elongated nuclei containing abundant cytoplasmic rough endoplasmic reticulum and well developed desmosome type intercellular junctions. Follow-up information ranging from 2 to 20 years was obtained in 18 patients. Six patients died of their tumors, whereas four patients died of unrelated causes without evidence of recurrence or metastases. Eight patients were alive with disease (recurrence and/or metastases) from 1 to 7 years after diagnosis. Four patients were alive and well without evidence of recurrence or metastases from 2 to 20 years (mean follow-up, 12.5 years). The present group of lesions appears to constitute a distinctive and as yet previously undescribed primary sarcoma of the lung, which probably represents the visceral counterpart of monophasic synovial sarcoma of soft tissue in a pulmonary location. Because of their distinctive biology these lesions should be distinguished from a variety of primary and metastatic malignancies of the lung.