Gemtuzumab Ozogamicin as Maintenance Therapy after Autologous Stem Cell Transplantation (ASCT) in Patients with Acute Myeloid Leukemia (AML).

The role of ASCT in AML appears to be appropriate in patients with favorable cytogenetic features whereas allogeneic SCT is appropriate in those with high-risk cytogenetic features. Gemtuzumab ozogamicin (GO), a monoclonal antibody conjugated to the calicheamicin, targets the CD33+ cell surface marker that is expressed on cells in the majority of AML patients. Clinical trials currently underway are investigating the role of GO in consolidation therapy. We hypothesized that GO could have beneficial effects as maintenance therapy after hematopoietic SCT in high-risk patients. Here we report data on 4 AML patients in CR who received 4 doses of GO as maintenance therapy following ASCT. Our approach differs from previous reports in the literature in that, instead of using GO to induce a first remission or re-induce a second remission after relapse, we administered GO to patients while they remained in remission, two months after undergoing ASCT. Patient #1 was a 64 year-old male with 88% CD33 expression at diagnosis. This patient had previously undergone an ASCT using a conditioning regimen of Bu+Cy. He was in second CR following an induction regimen of 2 cycles of fludarabine + cytarabine + idarubicin. Patient #2 was female, aged 67 years and had 90% CD33 expression at diagnosis. She was in first CR following an induction regimen of 2 cycles of etoposide + cytarabine + idarubicin. Patient #3 was a 69-year old male with 95% CD33 expression at diagnosis. He was in first CR following an induction regimen of 2 cycles of fludarabine + cytarabine. Patient #4 was a 59 year-old male with 93% CD33 expression. He was in first CR after a second line treatment with mitoxantrone, cytarabine and etoposide. Histocompatible donors were not available for any of the patients. Three months after attaining CR, all 4 patients received a myeloablative conditioning regimen with B(A)VC, Bu+Cy, Bu+Cy and TBI+Melphalan, respectively, and underwent ASCT. Two months after the ASCT procedure, patients initiated treatment with GO: GO was administered alone for 4 doses with 28 days between doses (two patients received 6 mg/mq for the two first doses and 3 mg/mq for the two last doses; two patients received 3 mg/mq for four doses). All four patients remain alive and in CR at +17, +13, +11and + 5 months. Overall survival at the time of reporting is +35, +15, +13 and +8 months in patients 1, 2, 3 and 4, respectively. There were no cases of grade 3 or 4 liver toxicity and bleeding was not observed in any of the patients. Thrombocytopenia (50,000–100,000 cells/μL) occurred in all four patients and neutropenia (500–1000 cells/μL) in two patients. In conclusion in our small series GO demonstrated good efficacy when administered in fractionated doses as maintenance therapy after ASCT in patients with CD33+ AML in first or second CR. GO showed an acceptable tolerability profile, with no severe hepatotoxicity and no bleeding. Thrombocytopenia occurred in all three patients and in all cases there was a rapid platelet recovery. A GO dose of 3 mg/m² appeared to be better tolerated than the higher dose (6 mg/m²) and will be used in future studies. If confirmed in a study involving a larger number of patients, our results could support a new therapeutic role for GO, namely as a maintenance therapy for patients in CR following hematopoietic SCT.