The MRD target a centre can run decides which infants are intensified, and the two targets disagree in the direction that matters
also called MRD platform risk · assay-driven allocation · MRD target discordance
Which leftover-disease test a hospital is able to run changes which babies get the most intensive treatment, because the two available tests disagree about roughly one child in ten at exactly the level where the decision is made. The disagreement is not random: the test that needs a specialist laboratory catches relapses the routine one misses.
The same thing, for a scientist
This is an allocation risk, not a biological one. In Interfant-06, applying the protocol cut-offs produced 19 patients positive by the KMT2A genomic breakpoint and negative by IG/TR, of whom 9 relapsed (6-year cumulative incidence of relapse 48.7%), against 12 positive by IG/TR and negative by KMT2A, of whom 1 relapsed (CIR 8.3%, P = .02) [E1]. Overall agreement was 94% of 223 samples with no significant discrepancy at end of induction [E1], so the disagreement is confined to the decision threshold - which is the only place it can do harm. In the infant flow-versus-fusion-transcript comparison, 12.5% of 942 marrow samples were discordant, with the molecular assay uniquely positive five times as often as flow [E2]. In paediatric B-ALL, moving from flow to sequencing at the same nominal threshold reclassified 38.7% more patients as MRD-positive [E3]. **The target a centre can run is determined by infrastructure**: the genomic breakpoint requires a referral characterisation service using LDI-PCR or KMT2A-targeted NGS [E4], while flow and Ig/TCR need neither. So the assay that Interfant-06 found better is the one least available, and the direction of the resulting misallocation is under-intensification of children whose disease only the specialist assay can see.
The mechanism of harm, in both directions
Under-intensification. A centre running Ig/TCR alone will classify 19 of every ~223-sample cohort's worth of patients as below threshold when the fusion target would have called them above it, and roughly half of those relapse 1. They do not receive myeloid-style consolidation or transplant consideration.
Over-intensification. The mirror group exists and is smaller and better-behaved: 12 patients positive by IG/TR and negative by KMT2A, 1 of whom relapsed 1. On a fusion-target-only strategy those 12 avoid intensification they probably did not need; on an Ig/TCR-only strategy they receive it. False positivity of IG/TR PCR targets in regenerating marrow is a described phenomenon and is the plausible mechanism 1.
Both errors land on infants under one year, for whom the intensification in question is anthracycline, etoposide and mitoxantrone, or busulfan-based allogeneic transplant. Treatment-related mortality in Interfant-06 was not negligible and induction mortality is a leading cause of death in this disease.
Why this is a structural inequity rather than a technical preference
The recommended target is produced by a small number of centres. The recombinome network describes samples being pre-screened at diagnostic centres worldwide and then sent to Frankfurt for LDI-PCR, LD multiplex PCR or KMT2A-targeted NGS, with the resulting idiosyncratic genomic fusion sequence made available to the sender for patient-specific MRD surveillance 4. Interfant-06 states the breakpoint was determined in Frankfurt or in Catania 1.
So an infant's MRD target depends on whether their treating centre is inside a network with shipping agreements, ethics approvals and funding to send diagnostic DNA to one of two European laboratories. Interfant-06 itself reports 6-year event-free survival 10-12 percentage points higher in West European and North American groups than elsewhere 5. That gap has many causes and this is plausibly one of the smaller ones, but it is one of the few that is addressable by logistics rather than by biology.
The mitigation that does not require the network is to run both available assays and use the higher value, which is what Interfant-06 did where both existed 1, and what the MLL-Baby group concluded from combining flow with fusion-transcript PCR 2. Combining two imperfect, locally available assays is a real option and the evidence supports it; recommending a target that a centre cannot obtain is not.
| kind | delivery |
|---|---|
| severity | moderate; affects allocation to myeloid-style consolidation and to allogeneic transplant in first remission in infants under 1 year |
| infrastructure dependency | genomic breakpoint targets are characterised at a small number of referral centres (Frankfurt, Catania named in Interfant-06); flow and Ig/TCR are locally available |
| mitigation | run both locally available assays and use the higher value, as Interfant-06 did where both targets existed and as the MLL-Baby group concluded from combining flow with fusion-transcript PCR; and pursue locally runnable targeted NGS to obtain a fusion target without a referral workflow |
affects
[ "concept-mrd-monitoring-genomic-breakpoint", "concept-mrd-monitoring-ig-tcr-rearrangement", "concept-mrd-flow-cytometry-and-the-lineage-switch-blind-spot" ]
discordance at decision threshold
{
"kmt2a_positive_igtcr_negative_n": 19,
"relapses": 9,
"cir_6y_pct": 48.7,
"igtcr_positive_kmt2a_negative_n": 12,
"relapses_2": 1,
"cir_6y_pct_2": 8.3,
"p_value": 0.02,
"source_pmid": "33405950"
}platform discordance rates
{
"flow_vs_fusion_transcript_infants_pct": 12.5,
"flow_vs_sequencing_reclassified_upward_pct": 38.7
}- Recommending the better MRD target without the infrastructure to deliver it converts a measurement problem into an equity problem, and the children who lose are in the countries whose Interfant-06 event-free survival was already 10-12 points lower.
- Using the higher of two discordant values is a rule that can only increase intensification. Applied to a population with meaningful treatment-related mortality, a rule that never de-escalates is not obviously conservative.
- The discordance is concentrated at the threshold, which is exactly where a protocol's allocation rule lives. A 94% overall concordance is reassuring about the assay and says nothing about the decision.
- Both MRD targets are DNA-based and both persist through a lineage switch. Neither the discordance analysis nor the intensification rule built on it addresses the case where the clone that survives is not the disease the intensification is aimed at.
- What proportion of infants with KMT2A-rearranged ALL worldwide have access to a genomic-breakpoint MRD target? The recombinome network lists contributing countries but nobody has published a denominator.
- How many patients, not samples, would be assigned to a different Interfant risk group by each of the available assay combinations? Every published comparison reports sample-level concordance and the clinically meaningful figure is patient-level reclassification.
- Can a locally runnable targeted NGS assay produce a usable patient-specific fusion sequence without the referral workflow, and at what DNA or RNA input from an infant marrow?
- Does using the higher of two discordant MRD values - the Interfant-06 rule - improve outcome, or does it simply intensify more children? The rule is sensible and has never been evaluated as a rule.
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
In Interfant-06, MRD by the KMT2A genomic breakpoint and by IG/TR rearrangements agreed in 94% of 223 samples with no significant discrepancy at end of induction, but at the protocol cut-offs 19 patients were positive by KMT2A and not IG/TR with 9 relapses and a 6-year cumulative incidence of relapse of 48.7%, against 12 positive by IG/TR and not KMT2A with 1 relapse and a CIR of 8.3% (P = .02); the breakpoint sequence was determined in Frankfurt or Catania and patient-specific primers were then designed and validated at national reference laboratories; and false positivity of IG/TR PCR targets in regenerating bone marrow has been described.
Clinical Implications of Minimal Residual Disease Detection in Infants With KMT2A-Rearranged Acute Lymphoblastic Leukemia Treated on the Interfant-06 Protocol. · Stutterheim J, van der Sluis IM, de Lorenzo P, et al. · J Clin Oncol 2021What this evidence cannot show
Read in full text. The 19-versus-12 comparison is post hoc with small numbers and wide confidence intervals (48.7%, 95% CI 23.8-69.7 versus 8.3%, 95% CI 0.4-32.6). It exists only among patients who had both targets, so it does not quantify the risk to patients who have only one. MRD was non-mandatory in the protocol, contributing a selection step before any of this.
Evidence that argues against this (1)
- The same study's primary agreement analysis found the two targets statistically interchangeable (P = .60 at end of induction, 7 of 90 samples differing by a log, 2 of those higher by IG/TR), so on average target choice does not change the measurement and the allocation risk is confined to the tail. Stutterheim J et al. 2021
- E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Across 942 bone marrow samples from 123 infants with KMT2A-rearranged ALL, flow cytometry and fusion-gene-transcript PCR were concordant in 87.4%, with 99 samples (10.5%) positive only by the molecular assay against 19 (2.0%) only by flow, and the most precise risk definition was obtained by combining the two methods.
Comparison of minimal residual disease measurement by multicolour flow cytometry and PCR for fusion gene transcripts in infants with acute lymphoblastic leukaemia with KMT2A gene rearrangements. · Popov A, Tsaur G, Verzhbitskaya T, et al. · Br J Haematol 2023What this evidence cannot show
One group's cohort on the MLL-Baby protocol with its own timepoints. Concordance is reported at sample level; the paper does not state how many patients would have been assigned to a different risk group.
Evidence that argues against this (1)
- The authors emphasise that most discordance occurred where residual leukaemia was close to the sensitivity limits, which means much of the 12.5% is analytical noise near zero rather than clinically consequential disagreement. Popov A et al. 2023
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
In 619 paired paediatric B-ALL marrow samples, high-throughput sequencing identified 55 (38.7%) more patients as MRD-positive than flow cytometry at a 0.01% threshold, and those discrepant patients had worse outcomes than flow-MRD-negative patients.
Measurable residual disease detection by high-throughput sequencing improves risk stratification for pediatric B-ALL. · Wood B, Wu D, Crossley B, et al. · Blood 2018What this evidence cannot show
Paediatric B-ALL, not infants and no KMT2A-rearranged subgroup; one of the two source trials selected patients on their flow MRD result. Cited here to show that platform substitution reclassifies patients at scale, not to make a claim about infants.
Evidence that argues against this (1)
- Five-year event-free and overall survival were similar for MRD-positive and MRD-negative patients by both methods at the 0.01% threshold, so reclassification at scale did not translate into a different average prognostic performance. Wood B et al. 2018
- E4established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
Genomic KMT2A breakpoint characterisation in the diagnostic network operates by pre-screening at local centres followed by shipment of genomic DNA to the Frankfurt Diagnostic Center of Acute Leukemia for long-distance inverse PCR, long-distance multiplex PCR or targeted next-generation sequencing, with idiosyncratic genomic DNA fusion sequences then made available to the sender of the sample for patient-specific MRD surveillance.
The KMT2A recombinome of acute leukemias in 2023. · Meyer C, Larghero P, Almeida Lopes B, et al. · Leukemia 2023What this evidence cannot show
Read in full text. This describes one network's workflow over two decades; other laboratories may perform breakpoint characterisation locally, and the paper does not enumerate which countries or centres have access. The listed contributing countries are predominantly European plus Australia and Brazil.
Evidence that argues against this (1)
- Targeted RNA-side NGS panels can identify partner genes and patient-specific fusion sequences from low RNA input without a specialist inverse-PCR workflow, so the infrastructure barrier is falling and a locally run NGS assay may make the fusion target obtainable outside referral networks. Afrin S et al. 2018
- E5established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
In Interfant-06, 6-year event-free survival and overall survival in West European and North American groups were 49.4% and 62.1%, which were 10% to 12% higher than in other countries.
Outcome of Infants Younger Than 1 Year With Acute Lymphoblastic Leukemia Treated With the Interfant-06 Protocol: Results From an International Phase III Randomized Study. · Pieters R, De Lorenzo P, Ancliffe P, et al. · J Clin Oncol 2019What this evidence cannot show
Abstract only; not open access and no PMCID returned by the Europe PMC core record. The abstract states the gap and does not decompose it, so attributing any part of it to MRD assay access is speculation, and it is flagged as such in the body of this entry.
Evidence that argues against this (1)
- Supportive care, infection mortality and protocol adherence are far more likely explanations for a 10-12 point survival gap than MRD target availability, and induction mortality and treatment-related death in infant ALL are large enough to account for it on their own. Pennella CL et al. 2020
- related to →MRD by genomic breakpoint: the only assay in this disease that is fusion-specific by construction
the target Interfant-06 preferred and the one least widely available
the locally available target that missed 19 patients at the cut-off
- related to →Which MRD timepoint drives which decision in infant ALL, and how good the evidence for each is
the decisions the discordance lands on
intensification here means ADE/MAE or busulfan-based transplant in an infant
- related to →Nine survivors in ten carry a long-term complication, and it is worse the younger they were
what over-intensification costs a surviving infant