PLAG1 Rearranged Soft Tissue Tumor in an Adult

Abstract

Abstract Introduction/Objective PLAG1 rearranged soft tissue tumor is a recently described entity in the pediatric population. Less than 10 cases have been reported identifying PLAG1 gene fusions with various gene partners. This tumor is characterized by spindled cells with low cellularity in fibromyxoid stroma, expressing CD34 and desmin. PLAG1 gene fusions have been identified in various other tumors, including lipoblastoma, salivary gland pleomorphic adenoma, myoepithelial tumors, uterine epithelioid and myxoid leiomyosarcomas, and chondroid syringoma. To our knowledge, we report the first case of a PLAG1 rearranged soft tissue tumor in an adult. Methods/Case Report A 32-year-old female with no significant medical history presented with a left thigh mass. MRI showed a 9.8 cm mass involving subcutaneous fat and causing marked sartorius muscle displacement. Resection showed a well-circumscribed, spindle cell tumor of low cellularity in a myxo-collagenous stroma. Bland, elongated, and ovoid-shaped spindled cells with occasional punctate nucleoli were seen. No mitoses or necrosis were identified. The tumor cells expressed CD34 and androgen receptors, partially expressed desmin and estrogen receptors, and focally expressed S100. MUC4 and beta-catenin were negative. Next-generation sequencing performed at Mayo Clinic Labs identified UBC::PLAG1 gene rearrangement. Results (if a Case Study enter NA) NA Conclusion To our knowledge, we describe the first case of PLAG1 rearranged soft tissue tumor in an adult. This case is also unique as the fusion partner gene, UBC, was not previously identified. All other cases reported occurred in those four years of age or younger, with one report in a 15-year-old female. Our patient has had less than six months of follow-up with no recurrence. With few cases reported, and relatively short follow-up periods thus far, the behavior of these tumors remains undetermined.