Abstract
BACKGROUND: Sarcomatoid carcinomas (SC) are rare tumors with both epithelial and mesenchymal characteristics, linked to aggressive behavior and poor prognosis. Sarcomatoid carcinoma of unknown primary (SCUP) is an exceedingly rare subset with limited literature and no standardized management guidelines. This study aims to characterize the clinical presentations, treatment patterns, and genomic landscape of SCUP. PATIENTS AND METHODS: Data were retrospectively collected from the Mayo Clinic Rochester Cancer of Unknown Primary Registry. Patients included had biopsy-proven SC with no identifiable primary tumor despite comprehensive diagnostic evaluations. Baseline characteristics, immunohistochemistry (IHC) results, next-generation sequencing (NGS) data, and treatment outcomes were analyzed. Statistical analyses included descriptive statistics, Kaplan-Meier survival estimates, and Cox proportional hazards regression. RESULTS: Fifty-two SCUP patients were identified, with a median age of 60 years. Most patients presented with widely metastatic disease, particularly lytic bone lesions. Elevated alkaline phosphatase (ALP) was noted in nearly half of the patients. IHC showed high positivity for AE1/AE3 and OSCAR antibodies. Tumor NGS revealed 247 alterations, with TP53 being the most common mutation. Patients receiving definitive therapy had a median overall survival (OS) of 72 months, significantly longer than those receiving systemic therapy (14 months). Immunotherapy was a significant prognostic factor, reducing the risk of death by 90%. CONCLUSIONS: This study provides essential insights into the clinical and genomic characteristics of SCUP, advocating for the integration of definitive therapy and immunotherapy in treatment protocols. Further prospective studies are needed to validate these findings and improve patient outcomes.