A Novel Prognostic Factor for Allogeneic Hematopoietic Stem Cell Transplantation Based on Bone Marrow Assessment on the Day of Stem Cell Transplantation

[Introduction] Many factors predicting the outcomes of allogeneic hematopoietic stem cell transplantation (HSCT) recipient have been reported so far and widely used to assess the potential risk of undergoing allogeneic HSCT. Residual disease is considered one of the risk factors in HSCT, and mainly evaluated by bone marrow aspiration before HSCT. However, disease statuses at the point of stem cell infusion potentially differ from that of pre-transplant evaluation depending on the sensitivity for conditioning therapy or proliferation speed of the blast. In this study, we assessed residual disease by bone marrow aspiration on the day of stem cell transplantation (called "day 0" of HSCT) in order to analyze the relationship between day 0 marrow statuses and HSCT outcomes.

[Methods] This study was designed as a retrospective observational analysis, and we collected the patients who received first allogeneic HSCT for hematological malignant diseases between 2010 and 2014. Extramedullary diseases were excluded from the analysis. All HSCTs were consecutive and performed in our center. Bone marrow aspirated material was examined histopathologically, and residual blasts were evaluated by specific markers by immunostaining. If it has detected residual blasts even if only a few cells, it was defined non complete remission (CR) on day 0 (abbreviated as "non-day0CR"). We divided the patients into two groups according to the existence of residual blast in bone marrow on day 0 of HSCT.

[Results] We analyzed 121 HSCT recipients including 35 with acute lymphoblastic leukemia, 3 with acute undifferentiated leukemia, 65 with acute myeloid leukemia, 17 with refractory anemia with excess blasts and 1 with blast phase of chronic myelogenous leukemia. The median follow-up of survivors was 983 days (range 330 - 2092 days), and overall survival (OS) was 72% (95% confidence interval: 63 - 79%) at 1 year after HSCT. In univariate analyses, age higher than median 44 year-old, non-CR at the time of pre-HSCT assessment, hematopoietic cell transplantation specific comorbidity index (HCT-CI) at least 1 point, reduced intensity conditioning, and non-day0CR were extracted as predictors of poor OS. With multivariate analysis, HCT-CI and day 0 marrow status were significantly associated with OS. Furthermore, when patients were limited to pre-transplant non-CR subgroup, the patients achieving complete malignancies-free state on day 0 showed comparable prognosis with those who maintained CR before conditioning (Figure 1). Relapse after allogeneic HSCT was observed in 31 patients, and cumulative incidence of relapse was 11% (95% confidence interval: 6 - 17%) at 1 year after HSCT. With univariate and multivariate analyses, there were significant differences between the patients with CR marrow and those with residual malignancies on day 0 (P = 0.002). There was no significant difference in non-relapse mortality between the two groups (P = 0.18).

[Conclusions] We showed that bone marrow status on day 0 was significantly associated with OS and cumulative incidence of relapse. To our knowledge, this is the first report about the association with day 0 marrow status and post-HSCT prognosis. A malignancies-free state on day 0 could predict favorable prognosis in allogeneic HSCT, and the patient with residual malignancies on day 0 had lower OS and higher relapse rate. For the patients with residual malignancies on day 0, rapid tapering of immunosuppressant or arrangement of scheduled donor lymphocyte infusion may improve the outcomes.

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