Primary Subcutaneous Synovial Sarcoma: First Reported Subcutaneous Case Showing TLE1 Immunoreactivity

Fusion-driven cutaneous and superficial mesenchymal and adnexal tumors-A clinicopathologic and molecular study of 15 cases, including a novel case of ACTB::ZMIZ2-rearranged adnexal carcinoma

BACKGROUND

While the list of fusion-driven soft tissue neoplasms is expanding rapidly, their importance among cutaneous and superficial mesenchymal and adnexal neoplasms remains poorly understood. This challenge is especially evident in cases with ambiguous histopathology that are difficult to classify based on morphology.

AIMS

Our goal was to investigate the benefits of next-generation sequencing in diagnosing complex cutaneous neoplasms.

MATERIALS & METHODS

Departmental archives were searched for fusion-driven cutaneous neoplasms. Slides were retrieved and clinical information including follow-up was obtained.

RESULTS

Fifteen cases occurred in eight female and seven male patients, with a median age of 26 years (range: 1-83) at diagnosis. Tumors involved the extremities (9), scalp (5), and head and neck (1). Predominant features included myoepithelial (5), nested spindled with clear cytoplasm (2), atypical adnexal/squamoid (2), small round blue cell (2), cellular spindled (3), and fibrohistiocytic morphology (1). Most frequently encountered fusions involved EWSR1 (6) fused to ERG (1), FLI1 (1), CREB1 (2), CREM (1), PBX3 (1), followed by PLAG1 (4) with LIFR (2), TRPS1 (1) and CHCHD7. Additional fusions encountered were YAP1::NUTM1, EML4::ALK, SS18::SSX1 (2), and a novel fusion: ACTB::ZMIZ2. Integration of histologic features and molecular findings led to final diagnoses of primary cutaneous Ewing sarcoma (2), soft tissue myoepithelioma (4), cutaneous syncytial myoepithelioma (1), cutaneous adnexal carcinoma (1), porocarcinoma (1), inflammatory myofibroblastic tumor (1), synovial sarcoma (2), clear cell sarcoma (2), and angiomatoid fibrous histiocytoma (1).

DISCUSSION AND CONCLUSION

Our results show that fusion testing can be a helpful diagnostic tool, especially in cases with unusual or uncommon morphology in superficial sites. Furthermore, it can allow for the identification of potential therapeutic targets in some instances.

Primary superficial synovial sarcoma: clinical and histopathological characteristics in eight cases with molecular confirmation

BACKGROUND AND AIMS

Synovial sarcoma (SS) is a spindled cell sarcoma demonstrating varying degrees of epithelial differentiation and characterized by a pathognomonic t(X;18) translocation. SS most frequently involves deep soft tissue of the extremities in young adults. Superficial SS involving dermis and/or subcutaneous tissue is exceedingly rare.

METHODS AND RESULTS

We identified eight cases of primary superficial synovial sarcomas across three tertiary institutions. All cases were confined to the dermis/subcutis based on imaging or gross and microscopic examination. The average patient age was 36 years (range 14-50). The average tumor size was 2.4 cm (range 0.9-3.9 cm) and lesions showed classic monophasic (n = 4) or biphasic (n = 4) morphology. All tumors expressed keratin AE1/AE3 and/or epithelial membrane antigen (EMA), but were negative for CD34. The diagnosis for each case was confirmed by molecular detection of t(X;18). Six of the eight cases were treated with curative excision while the other two received additional radiotherapy. Follow-up was available for six patients (mean 68 months, range 2-108 months) and no patient experienced recurrence or metastatic disease.

CONCLUSIONS

We present the largest series to date of primary superficial SS with molecular confirmation for all cases. SS should be considered when evaluating a cutaneous monomorphic spindle cell neoplasm.

Primary cutaneous synovial sarcoma-Sometimes the hoof beats are zebras

Synovial sarcoma accounts for 5% to 10% of soft tissue sarcoma and it typically presents as a deep soft tissue mass. Primary cutaneous presentation is exceptionally rare, with only isolated case reports. We report a case of primary cutaneous synovial sarcoma in a 58-year-old woman that presented as a nodule involving the left occipital scalp. A complete radiologic evaluation of the patient failed to reveal any other mass lesion. Histologic sections showed a densely cellular, diffuse spindle cell proliferation within the subcutis. The lesion was composed of uniform, plump spindled cells with nuclei and vesicular chromatin, arranged in haphazard fascicles. There was admixed hemorrhage and a hemangiopericytoma-like vasculature. Immunohistochemically, the spindled cells showed focal strong positivity for cytokeratin (CK) OSCAR, CK5/6, CK34BE12, and pan-CK. Fluorescence in situ hybridization was positive for a rearrangement of SYT (SS18), confirming the diagnosis of monophasic synovial sarcoma. Synovial sarcoma should be considered in the differential diagnosis of monomorphous spindle cell tumors, especially if the tumors have a hemangiopericytoma-like vasculature or express keratins. In such cases, confirmatory molecular testing should be performed to confirm the diagnosis.

Primary cutaneous solitary fibrous tumor with entrapped eccrine components

First described in the pleura, solitary fibrous tumor (SFT) was subsequently reported in a variety of organ systems. Compared to other anatomic sites, primary cutaneous and superficial SFTs are relatively rare. Although several histopathologic variants of cutaneous and superficial SFT have been described, a primary cutaneous SFT harboring glandular components has not hitherto been documented in the literature. The current case report describes a spindle cell neoplasm of the right finger in a female patient with characteristic morphologic and immunohistochemical features of a SFT. Unexpectedly, various glandular and ductal components were identified in the SFT. A few hyperplastic lobules of sweat glands demonstrating similar morphology as the intratumoral glandular components and composed of secretory coils displaying mucinous metaplasia and ducts were detected in the attached subcutaneous tissue, suggestive of an inductive or obstructive effect of the SFT on the eccrine units. The intratumoral glands and ducts were judged to represent entrapped benign eccrine components from the attached subcutaneous tissue. Since this variant of SFT with entrapped eccrine components could mimic many biphasic epithelial and stromal tumors, pathologists should be aware of this unusual variant of SFT to avoid potential erroneous diagnosis, particularly mistaken confusion with a biphasic synovial sarcoma.