Expansion of Non-Neoplastic Myeloblasts in Regenerative Bone Marrows Post Lymphoblastic Leukemia Therapy
Oluyomi Asojo, Nitin Karandikar, Jacqueline Emmons, Brian Levenson, Franklin Fuda. UT Southwestern, Dallas, TX
Background: In common practice, the upper limit of bone marrow myeloblast (BMM) counts enumerated by flow cytometry (FC) is considered as 1.2%. Even in regenerative marrows with or without G-CSF therapy, BMM expansion beyond 5% is thought to be indicative of a neoplastic proliferation. However, a formal analysis of post-treatment BM by FC has not been conducted. In this study, we assessed %BMM by FC following therapy for B-lymphoblastic leukemia/lymphoma (B-LL) and determined the significance of high counts.
Design: Post-therapy BMs from 397 B-LL cases from 2009-2012 were the focus of this study. BM specimens were analyzed by 4-color FC for multiple myeloid and lymphoid markers. For comparison with historic data, an additional 30 cases from 2004 were also evaluated. %BMM and presence of aberrancy/variation were noted. For cases with BMM greater than 5% we also collected morphologic and pertinent clinical information.
Results: In 397 Cases (2009-2012), the blast count ranged from 0-36% (mean 1.36%). 18 cases (4.5%) had >5% BMM (Range 5.1%-36%; Mean 11.03%) [Table 1]. All 18 cases were either day 15 or day 29 post-induction. Of the 18, 10 showed mild IP variation, mainly variable expression of CD38 and HLA-DR, which was also identified in cases with <5% BMM. The remaining 8 cases showed no IP variation. 10 cases for which follow up FC was available showed a progressive decrease in %BMM on subsequent samples. None of the patients developed a myeloid neoplasm, based on clinical follow up data. There was no detectable association between increased BMM and persistent B-LL. Of note, none of the cases (0/30) from 2004 showed >3.0% BMM [Table 1].