Favorable Outcomes of Acute Leukemia of Ambiguous Lineage Treated with Hypercvad: A Multi-Center Retrospective Study

Background: Acute leukemias of ambiguous lineage (ALAL), including acute undifferentiated leukemia and mixed phenotype acute leukemia (MPAL), are rare hematologic malignancies, accounting for only 2-5% of cases of acute leukemia. Outcomes are generally poor, and retrospective studies have suggested that patients have better outcomes when treated with regimens used for acute lymphoblastic leukemia (ALL) rather than acute myeloid leukemia (AML). Due to heterogeneous definitions and rarity of these leukemias, no single ALL regimen has been studied extensively. Hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone (hyperCVAD) is one of the most widely used adult ALL regimens in the United States. We retrospectively examined the effectiveness of this regimen as initial therapy in patients with ALAL.

Methods: We retrospectively reviewed records from adult patients treated initially with hyperCVAD-based chemotherapy for ALAL as defined by the World Health Organization at five academic institutions. Only patients whose diagnosis was verified at a participating institution were examined. Philadelphia (Ph) chromosome-positive ALAL patients treated concurrently with tyrosine kinase inhibitors were included. The primary objective of the study was to determine the overall response rate (ORR) and median overall survival (OS). Descriptive statistics were used for baseline characteristics and responses, and Kaplan-Meier estimates were used to calculate all time-to-event outcomes.

Results: Twenty-two patients were identified, and pre-treatment characteristics are shown in the Table. Median age was 50 years (range, 22-69), with an even distribution of male and female patients (50% each). The majority (77%) were Caucasian. Two patients (9%) had acute undifferentiated leukemia, 11 (50%) T/myeloid MPAL, 8 (36%) B/myeloid MPAL, and 1 (5%) B/T MPAL. Seven (32%) had a complex karyotype (at least 3 abnormalities), 6 (27%) had a normal karyotype, 3 (14%) were Ph-positive and were treated concurrently with dasatinib, and 1 (5%) had an 11q23 rearrangement. FLT3-ITD was detected in 5 of 8 patients (63%) with an available mutation panel. Three (15%) had central nervous system (CNS) involvement at presentation, and one additional patient developed CNS disease during the course of therapy.

There were no deaths within the first 30 days, and the median number of cycles given was 4 (range, 1-8). The CR rate was 73% (n=16) and an additional 14% (n=3) had CR with incomplete count recovery (CRi), for an ORR rate of 86%. One patient had a partial response, and 2 patients had no response. Of the 19 patients achieving CR or CRi, median number of cycles to CR was 1.5, and 12 (63%) proceeded to allogeneic hematopoietic stem cell transplantation (alloHSCT). Of the 7 responders who did not receive alloHSCT, 3 relapsed shortly after initial CR and 4 are alive and in remission 77, 39, 37 and 10 months from treatment initiation. All 3 patients with Ph-positive disease achieved CR. Only 1 proceeded with alloHSCT and all 3 patients are alive and in remission at 51, 39, and 10 months. With a median follow up of 37 months, 14 (64%) patients were alive and in remission, including 11 who had undergone alloHSCT. Four of the 6 patients who died had a complex karyotype. Median overall survival for the entire cohort was not reached (Figure).

Conclusions: HyperCVAD results in high remission rates in patients with ALAL, with low incidence of early mortality and high ability to proceed to allogeneic transplantation following response. HyperCVAD can be considered an effective front-line therapy for patients with ALAL. Additionally, hyperCVAD may be a backbone for incorporation of novel immunotherapies and targeted therapies, which may improve results in patients with appropriate targets.

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