7109 Background: The frequency and clinical significance of secondary thrombocytopenia following initial engraftment in autologous hematopoietic progenitor cell transplantation (HPCT) is unknown. Methods: An IRB-approved retrospective study of thrombopoiesis in 359 patients transplanted with autologous blood (97%) or marrow (3%) who achieved transfusion-independent platelet engraftment to >50,000/mcL. Idiopathic secondary post-transplant thrombocytopenia (ISPT) was defined as >50% decline in blood platelets to <100,000/mcL in the absence of relapse or sepsis. Results: 62 of 359 study subjects (17%) met the criteria for ISPT within the first 100 days post-transplant. Patients with ISPT had more rapid platelet engraftment (17 + 5 days) versus non-ISPT patients (18 + 18 days; p=0.002) and partial recovery of platelet counts (median 96K/mcL) by day 75 post-transplant. The median survival for the entire population was 6.2 years with shorter survival in AML (1.3 years), breast cancer (6.2 years) and myeloma (5.5 years) than lymphoma patients (median not reached). Co- variates associated with post-transplant death (p<0.1) were entered into a multivariable logistic regression analysis stratified by cancer diagnosis at the time of transplant. Three factors were independently associated with worse survival: the number of prior chemotherapy regimens, failure to achieve a normal platelet counts post-transplant, and the occurrence of ISPT. A prognostic score was developed based upon the occurrence of ISPT and post-transplant platelet counts of <150,000/mcL. Survival of patients with both factors (n=25) was poor (15% alive at 5 years); patients with one factor (n=145) had 49% 5-year survival; patients with 0 factors (n=189) had 72% 5-year survival. Patients who failed to achieve a normal post-transplant platelet count received significantly fewer CD34+ cells/kg (P<0.001), while patients with ISPT received fewer CD34+CD38- cells/kg (P=0.001). Conclusion: ISPT reflects poor engraftment with long-term-repopulating CD34+ CD38- stem cells. The quantity and quality of autologous HPC in the graft are important prognostic variables for long-term survival. No significant financial relationships to disclose.
Long-Term Follow-Up After Allogeneic Hematopoietic Progenitor Cell Transplantation In Pediatric Patients-Multicenter Study
