Real-World Effectiveness and Safety of Hetrombopag for Delayed Platelet Engraftment Post-Allogeneic Hematopoietic Stem Cell Transplantation

Background: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) serves as a critical therapeutic approach for various malignant and non-malignant hematopoietic disorders. Notwithstanding successful hematopoietic recovery in most patients following allo-HSCT, a subset may encounter delayed platelet engraftment (DPE), a prevalent and potentially serious complication that stems from myeloablative conditioning. Occurring in approximately 5%-37% of allo-HSCT recipients, DPE is a known harbinger of increased transplant-related mortality and diminished quality of survival. Despite its clinical significance, a well-established standard treatment protocol for post-allo-HSCT DPE remains elusive. Multiple platelet transfusions, often administered in such cases, not only exacerbate the economic burden but also induce toxicities, thereby undermining the patient's quality of life. An alternative to platelet transfusion lies in the utilization of thrombopoietin-receptor agonists (TPO-RAs), advocated for enhancing platelet engraftment. These agents interact with the thrombopoietin receptor, stimulating intracellular signaling pathways inclusive of JAK/STAT, PI3K/AKT, and ERK1/2, which in turn, promote megakaryocyte proliferation and differentiation, thereby augmenting platelet production. Hetrombopag, a novel, orally administered, non-peptide, small-molecule TPO-RA, has been validated to effectively boost platelet engraftment and reduce the necessity for platelet transfusions post-allo-HSCT in a pilot study. Our study sought to investigate the effectiveness and safety of hetrombopag in treating DPE following allo-HSCT within a real-world setting.

Methods: In this retrospective study, we evaluated adult patients with hematopoietic disorders who underwent allo-HSCT and subsequently experienced DPE in our center, treated with hetrombopag between March 2022 and April 2023. Given the lack of a consensus definition, we deemed DPE as a platelet count (PLT) < 20 × 10 ⁹/L or a significant and rapid decreasing trend past day 28 post-allo-HSCT. Hetrombopag dosages of 2.5 mg, 5 mg, or 7.5 mg/day were prescribed based on individual patient conditions. Response criteria post-treatment were as follows: complete response: PLT > 50 × 10 ⁹/L without platelet transfusion; partial response: PLT between 20 and 50 × 10 ⁹/L without platelet transfusion; no response: PLT < 20 × 10 ⁹/L.

Results: A total of 20 patients were included in the analysis, with a median age of 52, and 60% of them were male. Hetrombopag administration commenced at a median of 58 days following allo-HSCT at a median dose of 5 mg/day, with a median treatment duration of 44 days. The initial platelet count was 24.5 × 10 ⁹/L and serum ferritin levels stood at 3351.1 ng/mL. Post-hetrombopag treatment, platelet counts escalated to 67.5 × 10 ⁹/L while serum ferritin levels decreased to 2726.0 ng/mL. Of the 20 patients, 13 patients (65%) exhibited a complete response, 6 patients (30%) achieved a partial response, and 1 patient (5%) displayed no response. Hetrombopag was well tolerated with only 5 patients reporting increased alanine aminotransferase/aspartate aminotransferase or total bilirubin levels (all grade 1 or 2), and the association with hetrombopag was undetermined.

Conclusion: Our findings suggest that hetrombopag yields a sustained response with acceptable tolerability in patients who experienced DPE following allo-HSCT, and could potentially offer a novel approach for managing such patients. Future large-scale, prospective studies are warranted to further assess the potential benefits of hetrombopag for improving patient outcomes following allo-HSCT.