A Multi-Institution Comparison of Mitoxantrone, Etoposide and Cytarabine (MEC) Vs High-Dose Cytarabine and Mitoxantrone (Ara-C Couplets) Therapy for Patients with Relapsed or Refractory Acute Myeloid Leukemia

Background:

Relapsed or refractory acute myeloid leukemia (R/R AML) portends a poor prognosis, thus salvage chemotherapy is commonly used as a bridge to HSCT, however the optimal salvage regimen remains unknown. For decades cytarabine (Ara-C) has served as the backbone of regimens frequently used in the R/R setting. MEC is among the most studied regimens for R/R AML; up to 66% of patients achieve complete remission (CR), with a median survival of 36 weeks (Arcese et al., J Clin Oncol. 1991). The Ara-C couplets regimen was shown to have a similar overall response rate (ORR) of 55%, in a single study (Larson et al., Leukemia & Lymphoma. 2012). Currently, there are no studies directly comparing these regimens. Here, in a multi-institution retrospective analysis we assessed the efficacy and toxicity of MEC and Ara-C couplets therapy.

Methods:

We analyzed the records of 136 patients treated between 1998 and 2017. There were 87 patients (15 from University of Illinois and 72 from Indiana University) treated with MEC (mitoxantrone 8 mg/m² IV, etoposide 80 mg/m² IV and Ara-C 1 g/m² x 5 days) and 49 patients (36 from University of Illinois and 13 from University of Chicago) treated with Ara-C couplets (mitoxantrone 30 mg/m² daily and Ara-C dosed at 2 g/m² twice daily or 3 g/m² daily; both drugs given on days 1 and 5). The primary endpoint was comparison of response rates. Secondary endpoints included progression free survival (PFS), overall survival (OS), duration of hospitalization, hematologic and non-hematologic toxicities, and success in proceeding to HCT.

Results:

The median age of the MEC group was 52 years (yr) (range: 20-75 yr) vs 55 yr (22-75 yr) in the Ara-C couplets group. There were significantly more white patients in the MEC group (72% vs 41%; p = 0.004). The incidence of unfavorable cytogenetics was similar between groups; 32 in the MEC group (36.8%) and 19 in the Ara-C couplets group (38.7%). High-risk patients, as defined by Charlson Comorbidity Index (CCI) ≥4, comprised 29 of 87 (33.3%) of MEC, and 26 of 49 (53.1%) of Ara-C couplets patients (p = 0.03). Time from initial diagnosis to diagnosis of R/R AML was similar between groups, 303 days (MEC) and 306 days, respectively (p = 0.10).

CR or CRi (ORR) was achieved in 44% of MEC, and 55% of the Ara-C couplets patients. OS was 159 days and 186 days, respectively (p = 0.055). PFS was 66 days in the MEC group and 113 days in the Ara-C couplets group (p = 0.56). In total, 27 (31%) of the MEC patients and 24 (49%) Ara-C couplets patients underwent HCT (p = 0.04). Within the MEC group, the median number of days to ANC and platelet recovery was 34 days and 35 days, respectively. ANC and platelet recovery was slightly longer within the Ara-C couplets group, at 41 days and 55 days, respectively (p = 0.02 for platelet recovery). The median duration of hospitalization was similar, 29 days for MEC and 30 days for Ara-C couplets.

The most common adverse event was febrile neutropenia (FN), occurring in 93% of the MEC and 78% of the Ara-C couplets patients (p = 0.01). Notably, grade 3/4 GI toxicity occurred in 15 MEC (17.2%) and one (2.0%) of the Ara-C couplets patients (p = 0.01). There were no significant differences between groups in terms of pulmonary, liver, renal, cardiac or neurologic toxicities.

Conclusions:

This is the first large multi-institutional retrospective study directly comparing salvage regimens in a racially diverse population of R/R AML patients. While matched for a number of variables (including the incidence of unfavorable cytogenetics), patients receiving Ara-C couplets did have a significantly higher CCI. Despite this, use of the Ara-C couplets regimen resulted in improved ORR, significantly improved efficacy as a bridge to HCT, and led to a significant comparative decrease in the incidence of FN and grade 3/4 GI toxicities. Our retrospective analysis suggests that this regimen should be considered as an effective, safe salvage regimen in this population.