Limitations of fibrosis grade as diagnostic criteria for post polycythemia vera and essential thrombocytosis myelofibrosis.

BACKGROUND

The clinical phenotype of patients with myeloproliferative neoplasms (MPNs) including primary myelofibrosis (PMF), polycythemia vera (PV), and essential thrombocytosis (ET) whom manifest WHO grade 1 marrow fibrosis is poorly defined. Current IWG-MRT criteria require 2+ marrow fibrosis for diagnosis of post PV/ET myelofibrosis (MF). In contrast, the 2008 WHO definition of PMF does not require a minimum fibrosis threshold.

METHODS

We retrospectively analyzed the clinical characteristics of 91 MPN patients with 1+ marrow fibrosis. We compared the clinical phenotype of sub threshold fibrosis PV/ET with that manifested by PMF. We applied the IWG-MRT criteria for post-PV/ET MF with the fibrosis component omitted and evaluated for percentage of criteria fulfillment.

RESULTS

When IWG-MRT criteria were applied to the PV/ET group, 38/58 (66%) of patients fulfilled criteria for diagnosis of post-PV/ET myelofibrosis except for the 2+ fibrosis requirement. Comparison of sub threshold fibrotic PV/ET clinical phenotype to PMF revealed similar characteristics including heavy symptomatic burden (57% and 52%), presence of splenomegaly (43% and 55%), leukoerythroblastic blood smear (38% and 45%), and median hemoglobin (12.8g/dL and 11.1g/dL).

CONCLUSION

MPN progression represents a biological spectrum and definitions of progression in ET/PV may benefit from criteria not restricted by degree of fibrosis.