SAN DIEGO—Pediatric patients with mixed phenotype acute leukemia (MPAL) can achieve minimal residual disease (MRD) negativity with acute lymphoblastic leukemia (ALL)-directed chemotherapy, according to new research.
In a retrospective study, most pediatric MPAL patients who received ALL-directed chemotherapy achieved an MRD-negative complete response (CR).
Ninety-three percent of patients achieved a CR at the end of induction with an ALL regimen, 70% were MRD-negative at the end of induction, and 86% were MRD-negative at the end of induction or consolidation.
Etan Orgel, MD, of the University of Southern California, Los Angeles, presented these findings at the ASH 2018 Annual Meeting (abstract 558*).
The study included 94 patients aged 1-21 years who met World Health Organization MPAL criteria and were treated between 2008 and 2016 at one of six U.S. institutions.
Most patients had B/Myeloid phenotype (89%, n=84), 10% (n=9) had T/Myeloid, and 1% (n=1) had B/T phenotype.
Eighty-seven patients (93%) received ALL induction, and 83 (89%) continued on ALL therapy after induction.
Ninety-three percent (81/87) of patients treated with an ALL induction regimen had a CR at the end of induction. One patient died during induction, and six had induction failures, defined as either disease progression (n=2) or MRD of 5% or greater (n=4).
The MRD-negative rates, defined as MRD less than 0.01%, were 70% (59/84) at the end of induction and 86% (68/79) at the end of induction or consolidation.
Twelve of 14 patients (86%) who were MRD-positive at the end of induction and continued on ALL therapy achieved MRD negativity at the end of consolidation.
The researchers assessed 5-year survival in patients who received an ALL regimen but did not go on to transplant.
In these patients, the 5-year event-free survival (EFS) was 75%, and the 5-year overall survival (OS) was 89%, “thus demonstrating that, for a majority of patients, transplant in first remission may not be necessary,” Dr. Orgel said.
“[T]his is very different from the approach used at many adult centers and many of the adult recommendations,” he added.
The 5-year EFS rate was 80% in patients who were MRD-negative at the end of induction and 52% in patients who were MRD-positive at the end of induction. Five-year OS rates were 91% and 84%, respectively.
The 5-year EFS rate was 77% in patients who were MRD-negative at the end of consolidation and was unavailable in the three patients who were MRD-positive. The 5-year OS rates were 89% and not available, respectively.
In a multivariable analysis, MRD was the strongest predictor of EFS (hazard ratio [HR]=3.5) and OS (HR=4.6).
There was a trend toward earlier failure and worse OS (HR=4.49, P=0.074) 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,” Dr. Orgel said.
In closing, he said this research suggests that ALL therapy without transplant may be sufficient to treat most patients with pediatric MPAL. However, he noted that clinical trials are necessary to prospectively validate MRD thresholds at end of induction and consolidation and to establish the threshold for favorable survival.
“Future research should explore either intensification of therapy or different therapies for patients with persistent MRD,” Dr. Orgel said.
He disclosed no conflicts of interest.
* Data in the presentation differ from the abstract.