Diagnostically Challenging Epithelioid Soft Tissue Tumors

Mesenchymal tumours with melanocytic expression: a potential pitfall in the differential diagnosis of malignant melanoma

Mesenchymal tumours with melanocytic expression can pose a diagnostic challenge because they frequently demonstrate both morphological and immunohistochemical overlap with other cutaneous melanocytic neoplasms. Therefore, they present potential pathological pitfalls that may lead to a misdiagnosis of malignant melanoma. Mesenchymal neoplasms that closely mimic melanoma include malignant melanotic nerve sheath tumour (melanotic schwannoma), epithelioid schwannoma, malignant peripheral nerve sheath, cutaneous syncytial myoepithelioma, clear cell sarcoma of soft tissue, and perivascular epithelioid cell tumour. Awareness of these melanoma mimics is necessary for establishing the correct diagnosis so that the appropriate clinical management can be rendered to the patient. This in-depth review highlights key diagnostic features and molecular genetics and also discusses the differential diagnosis and treatment of mesenchymal tumours that exhibit melanocytic expression.

Epithelioid Vascular Lesions: The Differential Diagnosis and Approach in Cytology and Small Biopsies

Vascular neoplasms are rare tumors with a multitude of clinical presentations and behavior, which make accurate identification and subclassification challenging on limited small biopsies. Within the spectrum of these lesions, the ones with epithelioid morphology, such as epithelioid hemangioendothelioma and epithelioid angiosarcoma, are particularly challenging given the morphologic overlap with nonvascular lesions and the limited cells due to hemodilution on sampling. Herein, we review the differential diagnosis of epithelioid vascular neoplasms, with a focus on the cytomorphology, differential diagnoses, and ancillary studies that pathologists should be aware of when evaluating small biopsies and aspirates, including novel translocations, and associated monoclonal immunohistochemistry antibodies, that can help in the diagnosis of some of these tumors. Awareness of these morphologic and ancillary study findings in these rare tumors will hopefully allow pathologists to recognize and render-specific diagnoses on limited samples of these challenging lesions.

Uncommon and peculiar soft tissue sarcomas: Multidisciplinary review and practical recommendations. Spanish Group for Sarcoma research (GEIS -GROUP). Part II

Among all Soft Tissue sarcomas there are some subtypes with low incidence and/or peculiar clinical behaviour, that need to be consider separately. Most of them are orphan diseases, whose biological characteristics imply a clearly different diagnostic and therapeutic approach from other more common sarcoma tumors. We present a brief and updated multidiciplinary review, focused on practical issues, aimed at helping clinicians in decision making. In this second part we review these subtypes: Alveolar Soft Part Sarcoma, Epithelioid Sarcoma, Clear Cell Sarcoma, Desmoplastic Small Round Cell Tumor, Rhabdoid Tumor, Phyllodes Tumor, Tenosynovial Giant Cell Tumors, Myoepithelial Tumor, Perivascular Epithelioid Cell Neoplasms (PEComas), Extraskeletal Myxoid Chondrosarcoma, NTRK-fusions Sarcomas. Most of them present their own radiological and histopathological feautures, that are essential to know in order to achieve early diagnosis. In some of them, molecular diagnosis is mandatory, not only in the diagnosis, but also to plan the treatment. On the other hand, and despite the low incidence, a great scientific research effort has been made to achieve new treatment opportunities for these patients even with approved indications. These include new treatments with targeted therapies and immunotherapy, which today represent possible therapeutic options. It is especially important to be attentive to new and potential avenues of research, and to promote the conduct of specific clinical trials for rare sarcomas.

18F-FDG PET/CT for Monitoring of Disease Progression in Metastatic Perivascular Epithelioid Cell Tumor

ABSTRACT

A 38-year-old woman presented for 18F-FDG PET/CT after multiple intra-abdominal surgical resections of a rare recurrent perivascular epithelioid cell tumor of the gastrointestinal tract. A solitary pelvic metastasis was detected, but surprisingly exhibited neither increased glucose consumption nor contrast enhancement on CT. Follow-up 18F-FDG PET/CT staging in the further disease course revealed multiple abdominal metastases, now, however, with markedly increased 18F-FDG uptake and intraoperatively correlating widespread peritoneal sarcomatosis. This case gives preliminary insight into monitoring of disease progression in metastatic perivascular epithelioid cell tumor, although the underlying pathophysiological bases for varying 18F-FDG uptake in PET/CT are not yet fully understood.

Malignant Epithelioid Soft Tissue Tumours- A Pathologist's Perspective With Review of Literature

Background Soft tissue tumours with epithelioid morphology have many differential diagnoses, which include epithelioid sarcoma, malignant extrarenal rhabdoid tumour, epithelioid malignant peripheral nerve sheath tumour, epithelioid leiomyosarcoma, epithelioid angiosarcoma and sclerosing epithelioid fibrosarcoma. There are other rare entities also. They often express characteristic patterns of immunohistochemical markers that can be used to identify these tumours. Materials and methods This retrospective study comprises 22 cases of malignant soft tissue tumours with epithelioid differentiation diagnosed over a period of four years. Findings regarding clinical presentation, cytological findings, histopathological findings and immunohistochemical profile of the tumours were noted and analyzed. Results A total of 22 cases were included in the study including five cases of epithelioid sarcoma (conventional and proximal), three cases of epithelioid angiosarcoma and epithelioid myxofibrosarcoma, two cases of epithelioid malignant peripheral nerve sheath tumour, epithelioid gastrointestinal stromal tumour and clear cell sarcoma each, one case of epithelioid leiomyosarcoma, sclerosing epithelioid fibrosarcoma, malignant extrarenal rhabdoid tumour, monophasic synovial sarcoma and malignant and malignant perivascular epithelioid cell tumour each. Conclusion Pathologists should be aware of the various differential diagnoses of soft tissue tumours with epithelioid morphology. Over and above the clinical findings and morphological features, ancillary methods like immunohistochemistry help to arrive at a definitive diagnosis in most cases.

A case of primary distal-type epithelioid sarcoma of the lumbar vertebra with a review of literature

Epithelioid sarcoma (EpS) is a rare malignant neoplasm that accounts for < 1% of adult soft tissue sarcomas. Primary EpS of the bone is extremely rare and only a few cases have been reported to date. We report a case of primary distal-type EpS of the lumbar vertebra. A 30-year-old man without any history of malignant tumors had complained of lumbago for 3 months before visiting the hospital. Magnetic resonance imaging (MRI) of the lumbar spine showed a high signal intensity on the fat-suppressed T2-weighted image (WI) and a low signal on the T1WI at the L1 vertebral body. The tumor protruded toward the anterior components. Systemic radiological examination revealed no other lesion. A biopsy revealed a primary malignant tumor with epithelioid features. After chemotherapy, total en bloc spondylectomy was performed. Macroscopically, the tumor replaced the entire L1 with necrosis. Histologically, the tumor showed nodules of epithelioid cells that were strongly positive for epithelial markers, but a lack of INI1 expression. Central necrosis in the tumor nodule was also observed. This tumor showed loss of heterozygosity at the SMARCB1 locus but without the SMARCB1 mutation. The result of Foundation One ®CDx showed no actionable mutations. Seven months after surgery, a subcutaneous metastasis to the left cheek and bilateral lung metastasis with pleural dissemination were observed on radiological examination. A final diagnosis of distal-type EpS was made based on these findings. The patient died of the disease 8 months after surgery.

TFE3-expressing malignant perivascular epithelioid cell tumor of the mesentery: A case report and review of literature

BACKGROUND

Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal tumor that exhibits an epithelioid and spindle cell morphology. The tumor is characterized by immunoreactivity for melanocytic and myogenic markers but can be misdiagnosed as more common tumors with similar characteristics, including gastrointestinal stroma tumors or leiomyosarcomas. Recently, a subset of PEComas has been reported to harbor a transcription factor binding to TFE3 fusion. Herein, we report a rare case of TFE3-expressing malignant PEComa arising from the mesentery.

CASE SUMMARY

A 50-year-old woman presented with abdominal discomfort for 3 months. Results of laboratory tests were all within the normal ranges, and the patient had no notable medical history. Magnetic resonance imaging revealed a large tumor on the right side of the pelvic floor, which was originally suspected to be a primary ovarian tumor. However, during surgery, the tumor was revealed to have originated from the mesentery. Histologically, the tumor was composed of bundles of spindle cells and sheets of epithelioid cells. Extensive coagulative necrosis and numerous mitotic figures were observed. Immunohistochemistry revealed that the tumor cells were positive for smooth muscle actin, HMB-45, and TFE3 expression. Tumor involvement of the rectal serosa was identified, leading to a final diagnosis of malignant PEComa of the mesentery. Surgical resection was followed by adjuvant chemotherapy. No recurrence or metastasis was observed over a 6-month follow-up period.

CONCLUSION

Malignant PEComa of the mesentery is extremely rare and should be distinguished from morphological mimics through differential diagnosis and immunohistochemistry.

Clear cell sarcoma of soft tissue in pleural cavity: A case report

BACKGROUND

Clear cell sarcoma (CCS) of soft tissue is a rare malignant soft tissue sarcoma usually reported to locate at distal end of extremities and rarely at trunk. Herein, we report a case of CCS in pleural cavity.

CASE SUMMARY

A 31-year-old male was admitted for an uncertain mass in left pleural cavity in routine physical examination without any symptoms. A VATS surgery was performed to remove the tumor. The pathological finding displayed a cystic mass with 6.5 cm at the longest diameter, dark red in section and cysts could be found locally. A strong expression of S-100, HMB45 and Vimentin was detected in immunohistochemical staining, which was inclined to the diagnosis of the CCS of soft tissue. The patient refused chemotherapy, radiotherapy and targeted therapy because of the personal financial situation. Follow-up computed tomography scans were done at the 90^th postoperative day and the 180^th postoperative day, and no obvious sign of recurrence was found till now.

CONCLUSION

CCS of soft tissue also can be found in pleural cavity although in an extremely rare incidence. Radical resection is useful to improve the prognosis.

Limited biopsies of soft tissue tumors: the contemporary role of immunohistochemistry and molecular diagnostics

Diagnosing soft tissue tumors is challenging, even on ample incisional biopsies or resection specimens. There are more than 100 distinct types of soft tissue neoplasms, including more than 80 benign and intermediate mesenchymal tumors and around 40 soft tissue sarcomas. Accurate diagnosis relies first upon recognition of characteristic histologic and cytologic features, including architecture, stromal characteristics, vascular patterns, and dominant cytology; these features may not be represented or apparent in limited core needle biopsy or fine needle aspiration specimens. Once a differential diagnosis is established, application of immunohistochemistry and cytogenetic or molecular diagnostic assays (especially fluorescence in situ hybridization) is used in an attempt to reach a specific diagnosis. In recent years, the diagnostic armamentarium for soft tissue tumors has expanded dramatically, following the discovery of molecular alterations that underlie the pathogenesis of soft tissue tumors. These include new diagnostic immunohistochemical markers that serve as useful surrogates for molecular genetic alterations. Availability of such markers has improved our ability to render accurate and specific diagnoses based on limited biopsy samples. In this review, examples of recently developed markers for the diagnosis of selected soft tissue tumor types will be discussed, including solitary fibrous tumor (STAT6), malignant peripheral nerve sheath tumor (H3K27me3), epithelioid hemangioendothelioma (CAMTA1), dedifferentiated liposarcoma (MDM2), and CIC-DUX4 sarcoma (WT1 and ETV4).