Comparison Of Plasma Cell Infiltration In Random Samples Of The Bone Marrow And Osteolyses Acquired By Ct-Guided Biopsy In Patients With Symptomatic Multiple Myeloma.

8040 Background: The degree of plasma cell infiltration in bone marrow is an important diagnostic and prognostic marker in multiple myeloma. An infiltration of 60% or more has been included into the new criteria of the International Myeloma Working Group defining myeloma necessitating systemic treatment. However, malignant plasma cells infiltrate the bone marrow in different patterns. While some patients show focal accumulations others present with a diffuse or a mixed pattern. Usually bone marrow examination is performed on a random sample from the pelvis or sternum as regions where bone marrow can be reached most easily. It is unclear if the plasma cell percentage of this particular location is really representative for the whole bone marrow compartment. Methods: To investigate the differences between plasma cell infiltration of the bone marrow in random samples compared to that in focal lesions, we performed immunohistochemistry on conventional bone marrow trephines of the iliac crest and on samples from CT-guided or open biopsies of osteolyses in 31 patients with symptomatic multiple myeloma at first diagnosis, respectively. Results: Location of guided biopsy was outside the pelvis in 4 and from an osteolysis in the pelvis in 26 patients. A median plasma cell infiltration of 30% (0 - 90%) was found in the random sample. In the osteolyses median infiltration was 60% (0 - 100%). From 21 patients with a plasma cell percentage of less than 60% in the random sample 10 (48%) showed 60% or more plasma cells in the osteolysis. Conclusions: Routinely performed random sample of the iliac crest might underestimate the degree of plasma cell infiltration in the whole skeleton. This ongoing study will also address the question if malignant plasma cells in osteolyses are genetically different from those from the random sample.