Precision of histological bone marrow staging in follicular Lymphoma and diffuse large B-cell Lymphoma

Introduction: In Non-Hodgkin Lymphoma (NHL), bone marrow histology is the gold standard against which ancillary investigations such as immunophenotyping and gene rearrangement studies are interpreted. There is currently no data on the reproducibility of histological findings. This study was conducted to determine the rates of inter- and intraobserver agreement in histological detection of bone marrow involvement in the two major subtypes of NHL, Diffuse Large B-cell Lymphoma (DLBCL), and Follicular Lymphoma (FL). Methods: The bone marrow slides of randomly selected DLBCL and FL cases were independently examined by two hematologists using standardized reporting criteria on two occasions at least two weeks apart. Samples included both aspirate and trephine biopsy slides. Weighted kappa statistics were used to examine agreement for the discrete measures. Results: Weighted kappa analyses showed variable inter-observer agreement in 38 DLBCL cases [aspirate=0.52; trephine= 0.77] and 38 FL cases [aspirate=0.48; trephine=0.77]. Conclusion: Overall, higher agreement rates were noted with trephine biopsies than with aspirates. Except for the high intra-observer agreement on trephine biopsy assessment in FL, there is poor agreement in histological staging of both FL and DLBCL which demonstrates the limitations of histological diagnosis and the futility of interpreting ancillary tests against histology.