European consensus on grading bone marrow fibrosis and assessment of cellularity.

TLDR

Bone marrow biopsy assessment relies on quantifying cellularity and fiber content, which are crucial for evaluating disease dynamics, risk stratification, survival, and therapy‑related changes, and for avoiding misinterpretation of fiber loss in fatty or edematous samples. A European panel of expert pathologists reviewed numerous trephine biopsy slides under a multi‑headed microscope, critically evaluating existing scoring systems to establish consensus grading criteria for cellularity and fibrosis. The consensus defined age‑dependent cellularity decline, simplified myelofibrosis grading into four reproducible categories distinguishing reticulin from collagen, and emphasized assessing fiber density relative to hematopoietic tissue, enabling precise grading throughout disease progression and post‑therapy.

Abstract

Quantification of characteristic bone marrow biopsy features includes basic parameters such as cellularity and fiber content. These are important to assess the dynamics of disease processes with a significant impact on risk stratification, survival patterns and, especially, therapy-related changes. A panel of experienced European pathologists and a foreign expert evaluated, at a multi-headed microscope, a large number of representative slides of trephine biopsies from patients with myelofibrosis in an attempt to reach a consensus on how to grade cellularity and fibrosis. This included a critical evaluation of previously described scoring systems. During the microscopic analysis and subsequent discussion and voting, the importance of age-dependent decrease in cellularity was recognized. Grading of myelofibrosis was simplified by using four easily reproducible categories including differentiation between reticulin and collagen. A consensus was reached that the density of fibers must be assessed in relation to the hematopoietic tissue. This feature is especially important in order to avoid a false impression of a reduced fiber content in fatty and/or edematous bone marrow samples after treatment. The consensus for measuring myelofibrosis by clear and reproducible guidelines achieved by our group should allow for precise grading during the disease process and after therapy.