Association of Day +100 Platelet Count and Survival Post Allogenic Hematopoietic Stem Cell Transplantation

Introduction :

Recovery of platelet count by day 100 post allogeneic HSCT is reported to be a predictor of overall survival. Delayed platelet recovery could impact outcome due to its association with incipient disease relapse, graft failure, infection or other causes of treatment related mortality (TRM).

We investigated the correlation between day +100 platelet count and overall survival post allogeneic HSCT in pediatric cancer patients.

Methods:

This was a retrospective study of consecutive patients who underwent allogeneic HSCT at the Children Cancer Hospital Egypt (CCHE 57357) between 2009 and 2015 with a minimum follow up duration of one year post transplant. All eligible patients received myeloablative conditioning. All patients had matched related donors, except one with an unrelated cord blood donor. Patients who survived without relapse until day 100 post HSCT were divided into two groups: early platelet recovery (EPR) (platelet count >100x10⁹/L at day +100 post transplant) and delayed platelet recovery (DPR) (platelet count ≤ 100x10⁹/L at day +100 post transplant).

Results :

During the study period, 155 patients were transplanted for hematological malignancies: AML (58), ALL (38), mixed phenotype leukemia (5), CML (33), JMML (14), MDS (5), NHL (2). The median age at transplant was 10 years. Stem cell source was bone marrow in 92 patients (59.4%), peripheral blood stem cells in 58 patients (37.4%) and cord blood in 5 patients (3.2%) with median CD34+ stem cell dose 5.6 x 10⁶/kg.

At day+100, 40 patients (26%) had DPR, 113 patients (74%) had EPR (two patients were excluded: one died before day+100 and one was lost to follow-up). With a median follow-up of 41 months (Range 1 - 93 months), 43 patients (27.7%) died, 36 due to relapse, 6 from TRM and one unknown. The 3 year disease free survival (DFS) and overall survival (OS) was 68±7.84 % and 71.9±7.84 % respectively. For EPR patients, 25 (22%) died compared to 17 (42.5%) DPR patients. The 3 year overall survival was 77.9% and 57.1% for the EPR and DPR respectively (p 0.006). The 3 year DFS of the EPR and DPR groups were 73.2±9% and 54.8±16.3% respectively (p 0.02). Incidence of disease relapse for EPR and DPR patients was 22.6 %( 95%CI 15.1-31%) and 39.5(95% CI 23.7 - 54.8%) respectively (p 0.04). Multivariate analysis for survival identified delayed platelet recovery as a predictor of decreased survival (p 0.002) (HR 3.23 95% CI 1.56-6.66). Chronic GVHD, was also a significant predictor of decreased survival (p 0.044) (HR 2.54 95% CI 1.03-6.31).

Conclusion:

Platelet count at Day 100 is simple to obtain, inexpensive and routinely collected as part of clinical care. Platelet reconstitution is a complicated process and abnormal platelet counts can be due to many different reasons. Our results suggest that patients with a robust platelet count at Day 100 can be considered in a good risk category. However, patients failing to achieve a normal platelet count have inferior long term OS and DFS. Thus thrombocytopenia, regardless of etiology, can be used to identify a vulnerable group of patients who require close observation and may be considered for further diagnostic evaluation.