The Elucidating Pathways of Steatohepatitis (EPoS) staging system: A reproducible 7-tiered fibrosis scoring system in MASLD

Background & Aims: Fibrosis in metabolic dysfunction-associated steatotic liver disease (MASLD) is histologically staged using the 5-tiered NASH CRN system, which has limited resolution for advanced fibrosis stages that are strongly associated with liver-related outcomes. We developed and validated an expanded histological staging system designed to more accurately reflect the spectrum of MASLD fibrosis. Methods: Nine expert hepatopathologists from the Elucidating Pathways of Steatohepatitis (EPoS) Histopathology Group reviewed MASLD liver biopsies to define, by consensus, the fibrosis stages of a new histological scoring system. To assess validity, correlations with quantitative collagen proportionate area (CPA), enhanced liver fibrosis (ELF) score, and liver stiffness measurement (LSM) were evaluated. To assess inter-observer variability and intra-observer agreement, each pathologist independently reviewed 45 cases (glass slides) using the EPoS staging system. After three months, the same slides were digitized and re-evaluated by each pathologist, blinded to their previous assessments. Results: