Salvage of Primary Refractory Acute Leukemia (AL) with High-Dose Etoposide (VP) and Cyclophosphamide (CY) Followed by Early Stem Cell Transplantation (SCT): An Effective Treatment Strategy for AML but Not for All.

Primary refractory AL has a poor prognosis although some patients (pts) can be salvaged with allogeneic SCT. Induction of complete remission (CR1) with conventional chemotherapy prior to conditioning and SCT may improve long-term event-free survival (EFS). Between 03/91 and 10/03, 59 adults with primary refractory AL (defined as >15% marrow blast cells on day 30 of induction) were treated with VP 2.4 g/m² by 34 hr. IV infusion beginning on day 1 followed by CY 2.0 g/m² IV daily on days 3, 4 and 5 with hyperhydration (3 L/m²/d) as bladder prophylaxis. Six pts received VP 3.0 g/m² and 1 patient received CY 1.8 g/m² x 4 days. The study included 39 males and 20 females with a median age of 41 years (range 17–60). Diagnoses were AML (42 pts), ALL (13 pts) and biphenotypic AL (4 pts). Eleven pts (19%) presented with a WBC count > 50 x10⁹/L and MRC karyotype was favourable in 4 pts, intermediate in 34 pts and adverse in 20 pts; metaphase analysis failed in 1 patient. All AML pts had already received high-dose cytosine arabinoside (HIDAC) and either daunorubicin (DNR) (n=33) or mitoxantrone and VP (n=9). ALL pts had previously received DNR, vincristine and prednisone with (n=9) or without (n=4) L-asparaginase. Biphenotypic AL pts had been induced with HIDAC, DNR, vincristine and prednisone. Induction day 30 marrow blast count was > 40% in 35 pts (59%). The most common grade I/II non-hematologic toxicities of VP/CY were oral mucosal (44% of pts), GI (20% of pts) and hepatic (15% of pts); only one patient developed grade III/IV toxicity (pulmonary). Median time to recovery of ANC > 0.5 x10⁹/L and platelets > 20 x10⁹/L was 26 and 22 days, respectively. Three pts (5%) died prior to day 21 of VP/CY and were not evaluable for response (2 pts sepsis, 1 patient pulmonary hemorrhage). Twenty-four pts (43%) were also refractory to VP/CY but 32 pts (57%) entered CR1. Response rates were similar in AML (54%) and ALL/ABL (67%) (p=0.52) and analysis of baseline patient characteristics did not reveal any predictors of response to VP/CY. Twenty-nine of 32 CR1 pts proceeded to SCT (24 allogeneic, 5 autologous); five pts with AL refractory to VP/CY also underwent allogeneic SCT although all subsequently relapsed. Four of the autologous SCT pts relapsed with only one patient remaining alive in CR1. Estimated 5-year EFS for the entire cohort of pts is 23%. The only positive predictor of survival was male sex (p=0.03) and cytogenetic risk group did not influence outcome (p=0.69). In the allogeneic SCT group, 5-year EFS was 45% and was signficantly better for pts with AML (52%) compared to pts with ALL (14%, p=0.04). In conclusion, VP/CY is able to induce CR1 in the majority of pts with primary refractory AL. For pts with AML in CR1 that have a suitable donor, subsequent allogeneic SCT results in a favourable long-term EFS. Although pts with primary refractory ALL have a high CR1 rate with VP/CY, overall outcome for this subgroup remains poor.