Presence of bone marrow fibrosis in multiple myeloma may predict extramedullary disease.

We analyzed the incidence of bone marrow fibrosis in 91 newly diagnosed Japanese multiple myeloma (MM) patients and evaluated the impact of fibrosis on clinical characteristics and therapeutic outcomes. Thirty-four (37%) patients had greater than grade 1 bone marrow fibrosis. The presence of bone marrow fibrosis did not affect laboratory data, the percentage of plasma cells in bone marrow or cytogenetic findings. It also had no significant effect on response to initial treatment, engraftment after autologous hematopoietic stem cell transplantation or overall survival. Interestingly, the incidence of extramedullary disease at diagnosis was significantly higher in patients with bone marrow fibrosis (p = 0.006). Analysis of biological characteristics of MM cells revealed that expression of CD49e, an alpha5/beta1 integrin, was downregulated in MM cells derived from patients with bone marrow fibrosis (p = 0.026). When seven of the original 34 patients were re-evaluated for fibrosis grading after treatment, five (71%) showed a reduction in fibrosis. Our present findings suggest that the presence of bone marrow fibrosis may predict development of extramedullary disease in MM.