Addition of Gemcitabine to the Standard Reduced Busulfan and Cyclophosphamide (BUCY2) Pre Allogeneic Hematopoietic Stem Cell Transplantation Conditioning for Acute Lymphoblastic Leukemia

In the last decade, hematopoietic stem cell transplantation (HSCT) has become an efficient strategy for the treatment of high risk acute lymphoblastic leukemias. Lymphoid acute leukemias (ALL) are considered malignant clonal diseases of the hematopoietic stem cells, and represent a therapeutic challenge due to the high relapse rate and mortality using conventional chemotherapy regimens. Many studies have shown a decrease in relapse and an increase in overall survival with allogeneic HSCT, however, despite the fact that results in ALL have improved in the past years, achieving complete remission (CR) in approximately 75% of the patients, the relapse rate remains high and long term survival is lower than 50% depending on age and disease characteristics. On the other hand, it has been stated that relapse is higher when an allo-HSCT is performed in second CR, obtaining poorer results compared to performing HSCT in first CR, although better than chemotherapy alone (87% probability of relapse).

It is necessary to implement strategies that increase efficiency of pre transplant conditioning regimens in patients diagnosed with ALL undergoing an allo-HSCT in order to reduce relapse and increase overall survival. The hypothesis is that adding gemcitabine to the standard institutional conditioning regimen (reduced BUCY 2) in patients with ALL undergoing an allo-HSCT, the relapse free survival as well as the overall survival will improve, because it has been demonstrated in other malignant hematological diseases that gemcitabine plus two alkylating agents, facilitates synergism with busulfan and melphalan, inhibiting the DNA damage repair and causing a higher cytotoxic effect.