223 A Rare Case of Primary Hypopharyngeal Synovial Sarcoma: Challenges in Diagnosis

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Introduction/Objective Synovial sarcoma is a malignant mesenchymal neoplasm comprising approximately 8-10% of soft tissue sarcoma. It is exceptionally rare in the head and neck region, accounting for 0.1% of sarcomas. Methods/Case Report A 42-year-old male presented with 3 weeks worsening difficulty breathing and muffled voice. He reported a 30lb weight loss over that same period. Subsequent CT demonstrated a 4.9 x 4.3 cm hypopharyngeal mass causing severe airway narrowing. Biopsy of the lesion demonstrated a biphasic neoplasm composed of intermixed epithelial and spindle cell components. The epithelial component formed compressed glandular structures, whereas the spindle cell component showed a more primitive long fascicular growth pattern with increased mitotic activity (approximately 10 mitoses per 10 high-power fields). The epithelial component strongly expressed cytokeratin (CK7, AE1/AE3, CAM5.2) and EMA, with the spindled component showing less pronounced expression. Both components, however, demonstrated diffuse nuclear positivity for the molecular surrogate stains SSX-C-terminus and SS18-SSX. These findings were consistent with biphasic synovial sarcoma, FNCLCC grade 3. Results NA Conclusion Synovial sarcoma of the hypopharynx is rare and challenging to diagnose. Biphasic tumors can mimic carcinoma, requiring a high degree of clinical awareness. New molecular surrogate stains can be informative in cases for which molecular testing is not possible.