Integrated histopathological and molecular diagnostics reveal substantial diagnostic shifts in pediatric melanocytic tumors

BACKGROUND AND OBJECTIVES: Pediatric melanocytic tumors are rare and biologically heterogeneous. Distinguishing melanomas from Spitz-lineage tumors based on histomorphology alone is challenging and may lead to inadequate treatment. We aimed to characterize melanocytic tumors in pediatric patients enrolled in the German STEP registry and to assess changes in diagnosis after centralized integrated pathology review. PATIENTS AND METHODS: We analyzed patients ≤ 18 years with melanocytic tumors registered in STEP (2021-2025) who underwent centralized review. Histopathological and immunohistochemical findings were integrated with molecular analyses. Local diagnoses were compared with final referral diagnoses. RESULTS: Thirty-five patients were included; molecular analyses were necessary in 29 cases (83%). After centralized review and integrated diagnostics, 16 tumors (46%) were reclassified. Fusion-defined Spitz-lineage tumors increased from 14% at local diagnosis to 40%. Among patients ≤ 10 years, none of the tumors initially diagnosed as conventional melanoma retained this diagnosis. After centralized review, 14 cases were diagnosed as melanoma and one case as clear cell sarcoma. Fatal outcomes were documented in 5 patients with melanoma. All remaining patients were alive without evidence of disease progression at last follow-up. CONCLUSIONS: Centralized integrated diagnostics improves classification of pediatric melanocytic tumors and may help to avoid unnecessary invasive diagnostics or therapy while ensuring accurate identification of melanoma.