Molligan, Jeremy

ABSTRACTBackgroundDifferentiating metastatic melanoma from histologic mimics such as malignant gastrointestinal neuroectodermal tumor (GNET), malignant melanotic nerve sheath tumor (MMNST), and epithelioid malignant peripheral nerve sheath tumor (EMPNST) poses significant diagnostic challenges due to overlapping morphology and immunophenotypes. PRAME is a novel immunohistochemical marker increasingly used to distinguish melanoma from its mimics, but remains underexplored in these rare tumor types.MethodsPRAME immunohistochemistry was performed on four GNETs, seven MMNSTs, 10 EMPNSTs, 16 metastatic melanomas (including eight undifferentiated melanomas), and two MITF‐rearranged melanocytic tumors. PRAME expression was scored from 0 to 4+ based on the percentage of tumor nuclei showing moderate to strong staining.ResultsAll GNETs, MMNSTs, and MITF‐rearranged tumors were PRAME‐negative. EMPNSTs showed variable expression: six were negative (0–1), one equivocal (2+), and three positive (3–4+). Fifteen of 16 melanomas were PRAME‐positive. PRAME scores differed significantly among tumor types (p = 1.99 × 10−5). PRAME demonstrated high sensitivity and specificity for distinguishing metastatic melanoma from primary mimickers including GNET and MMNST, but low specificity in EMPNST (71.4%).ConclusionsPRAME reliably distinguishes metastatic melanoma from GNET and MMNST, supporting its use in this differential. However, its reduced specificity in EMPNST limits its standalone diagnostic value in this context, emphasizing the need for a multimodal approach.

Background: Malignant mesenchymal tumors involving the parotid gland are uncommon, characteristically aggressive, and little is known with few reports documented. Study Design: Retrospective case series. Setting: Single institution tertiary care center, 2010 to 2022. Method: Patients were identified from an institutional parotid tumor database. Patient history, demographics, pathologic diagnosis, treatment, and follow up were documented. Results: Eight patients were identified, 3 were males. The average age was 61 years old, and the most common tumors identified were pleomorphic sarcomas (3 patients). Presenting symptoms included: preauricular/cheek mass in 7 patients, facial pain (4), otalgia (4), aural fullness (3), and numbness (1). All patients received a parotidectomy, and 4 patients received adjuvant therapy of either radiation or chemoradiation. Post-operatively, there were 3 cases of distant recurrence, 2 cases of regional recurrence, and 1 case of local recurrence. There were 2 reports of death. Conclusion: Malignant mesenchymal tumors of the parotid are rare, represent varied histologies. Due to their aggressive nature, surgical resection with radiation and close follow-up may be an appropriate treatment regimen in controlling the disease.

Introduction Although osteosarcoma represents the most common primary malignant bone tumor in children, they comprise only 0.2% of all cancers. Osteosarcoma frequently involves long bones; however, 8% of osteosarcomas involve the skull or mandible. Osteosarcoma is generally categorized based on location within the bone (central, surface, or extraskeletal) and histological grade (high-grade or low-grade). Osteoblastic osteosarcoma is a central, high-grade subtype and may be difficult to diagnose; it may present similarly to osteoblastoma, another rare, but benign, type of osteoblastic bone tumor. In this report, we present a rare case of osteoblastic osteosarcoma involving the temporal-occipital skull. Study design Case report and systematic review. Setting Tertiary referral center. Results A 21-year-old male presented for assessment of a mass appearing over his left mastoid region, first noticed within the previous 12 months. He experienced growth of the lesion and pain that increased when pressure was applied to the mass. Results from fine needle aspiration and CT-guided core biopsy were positive for osteosarcoma, osteoblastic-type. Magnetic resonance imaging of the brain and skull base revealed the mass to be 2.8 cm in maximal diameter. Given a somewhat favorable location, the tumor could be completely excised en bloc with negative margins, and the patient subsequently received adjuvant chemotherapy. The patient is doing well at last follow-up 10 months after surgery, with no evidence of recurrence to date. Conclusion The temporal bone is an uncommon location for a primary osteosarcoma, and there are numerous conditions that could present in a similar manner. This case highlights this rare occurrence of osteoblastic osteosarcoma of the temporal bone without previous exposure to radiation. There are a limited number of similar cases in the literature, and our report serves to bring awareness to this potential diagnosis and considerations related to treatment.

AimsOssifying fibromyxoid tumour is a rare mesenchymal neoplasm predominantly affecting adults characterised by a multinodular growth pattern and the presence of a fibrous pseudocapsule with areas of ossification. Prompted by the recognition of a non‐ossifying ossifying fibromyxoid tumour with lipomatous differentiation which caused diagnostic difficulty, we sought to further explore cases of ossifying fibromyxoid tumour with non‐osseous heterologous elements.Methods and ResultsA search of our institutional and consultation archives revealed three additional cases that demonstrated lipomatous components and two cases with cartilaginous differentiation. RNA‐sequencing revealed fusions involving PHF1 (n = 4) or EPC1 (n = 1) in all (five of five) cases tested, including EPC1::PHC1 and JAZF1::PHF1 fusions, which have not been reported before in ossifying fibromyxoid tumour.ConclusionThese six cases expand the histomorphological spectrum of ossifying fibromyxoid tumour, introducing lipomatous differentiation as a hitherto undocumented feature. Awareness of these rare variants will ensure appropriate diagnosis and clinical management.