SAN DIEGO – The majority of pediatric patients with mixed phenotype acute leukemia (MPAL) who were treated with acute lymphoblastic leukemia (ALL)–directed chemotherapy achieved a minimum residual disease (MRD)–negative complete response by the end of consolidation, according to findings from a multicenter retrospective cohort study.
The cohort included 94 patients aged 1-21 years who met strict World Health Organization MPAL criteria and were treated between 2008 and 2016 at one of six U.S. institutions. Most had B/myeloid phenotype (89%), and 87 patients were treated with an ALL regimen, Etan Orgel, MD, reported at the annual meeting of the American Society of Hematology.
Of those 87 patients, 81 (93%) experienced an end-of-induction (EOI) complete response. One patient died during induction and six had induction failures, defined as either disease progression before EOI (two patients) or EOI MRD of 5% or greater (three patients), saidof the University of Southern California, Los Angeles, and Children’s Hospital Los Angeles.
The MRD-negative rates, defined as MRD less than 0.01%, were 70% at EOI and 86% at EOI or end of consolidation (EOC); 12 of 14 patients who were MRD positive at EOI and continued on ALL therapy achieved an EOC MRD-negative complete response, including 8 of 8 with EOI MRD of 0.01%-0.09% and 4 of 6 with EOI MRD of 1% or greater.
Event-free survival at 5 years in the 78 patients without hematopoietic stem cell transplant at first remission was 75%, and 5-year overall survival was 89%, “thus demonstrating that, for a majority of patients, transplant in first remission may not be necessary,” Dr. Orgel said. “This is very different from the approach used at many adult centers and many of the adult recommendations.”
Overall 5-year EOI event-free survival was 80% in the 59 patients who were MRD negative at EOI, and 13% in 25 patients who were MRD-positive at EOI. The corresponding overall survival rates were 91% and 84%.
Overall 5-year EOC event-free survival was 77% in 74 patients who were MRD negative at EOC and was unavailable in 3 patients who were MRD positive at EOC, although all three were salvaged. The corresponding EOC overall survival rates were 89% and “not available,” Dr. Orgel reported.
Multivariable analysis confirmed the predictive value of MRD at EOI (hazard ratio for event-free survival and overall survival, 3.77 and 3.54, respectively).
Of note, there was a possible trend toward earlier failure and a trend toward worse overall survival (HR, 4.49, P = .074) for T-lineage–containing MPAL.
“That indicates that this might be a group that needs careful scrutiny of which form of ALL therapy they receive,” he said.
MRD in pediatric MPAL is rare. Recent studies of MPAL biology show areas of similarity with ALL and AML, and while this could eventually help further subcategorize or classify the disease and lead to biology-driven therapies, it is important to know how to treat the disease today, Dr. Orgel said.
The evolving consensus is that ALL therapy is adequate for most MPAL, but there is no established threshold for MRD to enable a risk-stratified MPAL approach, he added.
The current findings suggest that ALL therapy – without hematopoietic stem cell transplant – may be sufficient to treat most patients with pediatric MPAL, Dr. Orgen reported, noting that clinical trials are necessary to prospectively validate MRD thresholds at EOI and EOC and to establish the threshold for favorable survival.
“Future research should explore either intensification of therapy or different therapies for patients with persistent MRD,” he said.
Dr. Orgel reported having no financial disclosures.
SOURCE: Oberley M et al. ASH 2018, .