Atypical teratoid rhabdoid tumor with extraneural metastases: a case report with genomic analysis.

Atypical teratoid/rhabdoid tumor (ATRT) is an aggressive malignancy localized to the neuroaxis. It predominantly affects infants and young children, with exceedingly rare occurrences in adolescents and young adults. While its central nervous system (CNS) dissemination is common, extraneural metastases are exceptionally rare. We present a case of brain ATRT in a 16-year-old patient who, 8 months after the initial remission, developed an extraneural relapse involving visceral and skeletal sites. This unusual presentation posed significant diagnostic challenges in differentiating relapse from a second primary rhabdoid neoplasm. Comparative genomic analysis using a multigene panel found identical mutations in both the primary CNS tumor and a relapsed lesion, confirming their common clonal origin and ruling out a second de novo malignancy. Our case underscores the importance of awareness about the possibility of systemic relapse of ATRT. To our knowledge, this is the first report of applying comparative genomic profiling to discriminate between metastatic relapse and a second primary. Larger studies are needed to validate this approach in diverse tumor types.