EWSR1-NR4A3 fusion

Although biopsy was inconclusive, a highly malignant tumor was suspected radiologically. The resected specimen was histologically diagnosed as extraskeletal myxoid chondrosarcoma by detection of EWSR1::NR4A3 fusion using fluorescence in situ hybridization.

Conclusively, EMC may manifest superficial or osseous lesions harboring EWSR1::NR4A3, under-recognized solid or anaplastic histology, and pan-Trk expression, posing tremendous challenges. Most TAF15::NR4A3-positive cases were >10 cm in size, i.e., the crucial independent prognosticator, while pathogenic KIT mutation rarely occurred.

Thus, the diagnostic utility of INSM1 is rather low. Two morphologically unique cases of non-EWSR1 rearranged EMC with an extremely rare pseudopapillary growth pattern are also reported.

Our analysis confirms that most cases of EMC are positive for INSM1. However, the diagnostic utility of this marker is limited by the fact that only 50% of cases show a strong INSM1 expression in most tumour cells. Furthermore, our study highlights that EMC with alternative gene partners may present with unusual morphology.

Molecular detection is an indispensable technique for diagnosing cellular EMCs. The KIT mutations noted in this case report may offer fresh insights into EMCs treatment options.

Five-year follow-up includes locoregional recurrences 3 and 5 years postoperatively as well as recent lung metastases status post metastasectomy (Figure 3.14, D) and is currently NED. This case is valuable given its extremely unusual presentation in bone and its variant fusion status, and it highlights the indolent but clearly malignant behavior of this rare translocation sarcoma.

Although focal EMA expression in extraskeletal myxoid chondrosarcoma has been well described in the literature, this case illustrates that these tumors are capable of more-diffuse expression of epithelial antigens. In the context of this patient's unique anatomic site of presentation and cellular morphology, this phenomenon poses a diagnostic pitfall to the unsuspecting pathologist.

Patient followed up with an orthopedic oncologist and is currently on sunitinib, considering future wide local excision. Soft tissue sarcomas are rare, comprising 1% of adult malignancies with EMC accountable for <2% of all soft tissue sarcomas... We reported this rare etiology, its pathology and the diagnosis of bilateral pulmonary opacities, found to be metastatic EMC.