EHA 2016

Specific mutations in leukaemia patients' blood predicts survival

Dr Klaus Metzeler - University of Munich, Munich, Germany

We studied a cohort of a little bit more than 100 AML patients who were all treated similarly on a phase III trial and we studied paired samples obtained at diagnosis and at complete remission. We performed targeted sequencing of 68 genes that are recurrently mutated in AML. We established which mutations were mutated at the time of diagnosis and then we went back to the remission samples and looked which of these mutations were still detectable in the remission samples. We found that a little bit more than a third of patients had detectable mutations although they were in a morphological complete remission and these patients with persisting mutations had significantly shorter relapse free and overall survival. Now the interesting thing is that patients with persisting mutations were significantly older than those without and when we look at these variables in a multivariant model we see that actually mutation persistence was a stronger risk factor for relapse than older patient age. So from that, although that of course doesn’t establish causality, we would create a hypothesis that the persistence of pre-leukemic clones may be one reason for the worse outcome that we observe in older AML patients.

That’s not just linked to deep disease responses?

You’re alluding the question of what are we detecting there. Are we detecting minimal residual disease, the AML clone which is still there, or are we detecting pre-leukemic clones? So there are a number of hints suggesting that we are not just seeing residual leukemic cells there. First of all, many of the mutations that we’ve found in the remission samples had allelic fractions that point towards them being present in a quite large fraction of the cells in our specimen. They had allelic fractions of 10-50%, so that’s 20-100% of the cells, so that’s not compatible with minimal residual disease. We also have MRD measurements by flow for a substantial part of our patients and those are actually similar for patients with and without persisting mutations. Then almost all of the patients where we found persisting mutations had additional mutations in the leukaemia sample that went away in the remission sample. So really what we find at remission isn’t just a residual part of the leukaemia but it’s a different, probably earlier, clone that persists.

These clones that do persist, could they be a target for gene sequencing therapies? If they are genetically distinct from whatever other samples have been collected?

That is of course the key question, what do we do with this finding. First of all, we have data from our cohort, preliminary data, showing that those patients who received an allotransplant during follow-up, the persisting clone went away after the allotransplant and then after an allotransplant the survival of patients with and without persistent clones before the transplant no longer was any different. So that would argue that an allotransplant can eliminate those clones. Of course persistent clones are often found in older patients and they may not be good transplant candidates so the question is can we use any other targeted treatments to eliminate persistent clones. We don’t know that yet and that needs to be addressed in clinical trials.

With these results in mind, how can you see them influencing clinical treatment of diagnoses now?

The next step that we need to do is to integrate our data with data on established risk factors such as MRD levels, pre-treatment genetic mutations, cytogenetics, and see how much really the information on persisting mutations adds to what we already know. We’re in the process of doing that, we also want to extend our patient cohort to get more data on that but that will be the first step. Right now if a doctor chooses to study persisting mutations in remission and finds a clone that is still there I would discuss with the patient the increased risk for relapse and I would then at least closely monitor this patient using available MRD techniques. If we see a sign of impending relapse I would discuss the option of an allotransplant, I wouldn’t take any decision only based on the detection of a persistent clone right now.

That answers all the questions I had prepared, is there anything else that you would like to add?

One other thing that is very important to understand is really how are those persisting clones related to the relapse that later occurs. Because also preliminary data from our cohort suggests that in most cases the clone that causes relapse is actually the same clone or a progeny of the original clone that was there. So if it’s the same clone basically that comes back then what is the role of that pre-leukemic clone that persists in between? How does that mechanistically facilitate the relapse? That’s going to be a very interesting question and we’ll try to address that in further studies.