Minimal Residual Disease
More than 85 per cent of children with acute lymphoblastic leukaemia (ALL), the most common childhood cancer, can be cured. While clinical remission is achieved initially in almost 100 per cent of patients, about a fifth of patients later suffer a relapse due to the persistence of small numbers of cancer cells throughout treatment (‘minimal residual disease’ or MRD).
Almost all current clinical trials for ALL depend upon the measurement of MRD to determine each child’s risk of relapse and subsequent treatment. We have developed one of the best methods to measure MRD for ALL patients and now provide MRD diagnostic testing for ALL patients enrolled on several clinical trials. We are also carrying out research to further improve our ability to predict the risk of relapse.
The broad aim of our research is to see MRD testing become part of the routine clinical management of all children with ALL, allowing treatment to be tailored to the individual according to the level of disease remaining in his or her body. With this goal in mind, all aspects of our MRD testing are subject to quality assurance.
This work would not be possible without collaboration with treating oncologists and staff at children’s hospitals who are members of the Australian and Zealand Children’s Haemotology and Oncology Group (ANZCHOG) that sponsors our international trials.
A/Prof Rosemary Sutton
The diagnostic tests used at Children’s Cancer Institute to measure MRD rely on the identification of unique genetic markers for each patient’s leukaemia and then developing the highly sensitive Real-Time Quantitative (RQ)-PCR based MRD tests to measure the markers. Markers can be measured even at very low levels, equivalent to one leukaemic blast cell in 100,000 normal bone marrow or blood cells.
Since 2002, treatment decisions for children newly diagnosed with ALL have been based on MRD testing performed to measure early response to chemotherapy. While children with ALL usually need treatment for 2 years with chemotherapy, the level of disease present in the early stages (after 2 weeks, 1 month and 3 months) provides a very good indication of whether standard chemotherapy will be sufficient to cure them. This makes MRD levels an important aspect of the clinical trials in deciding patient treatment. Patients with high MRD levels, equal to or more than five leukaemic cells in 10,000 after one month of treatment, are known to be at very high risk of relapse. As part of the Study 9 clinical trial, they are offered novel, more intensive chemotherapy and a bone marrow or cord blood transplant if a donor is available.
Patients in whom MRD levels drop very rapidly in response to treatment to undetectable levels after only one month of therapy have greater than 95 per cent chance of cure. They are usually defined as ‘standard-risk’ patients. Patients with low levels of MRD at this stage, which is the largest group, are usually defined as ‘medium-risk’ patients and have an average rate of relapses close to 20 per cent.
Following the successful treatment of most of the 607 children on the ANZCHOG Study 8 trial (2002-2011), eligible newly-diagnosed children with ALL since 2012 have been offered treatment on the Study 9 trial. This international trial is comparing slightly different treatment options in 5000 patients in 7 different countries. MRD is still being used to determine the level of risk that each patient has of relapsing. The main focus of this trial is to try to reduce the toxicity of treatment while maintaining effectiveness.
Monitoring response to treatment in high risk patients
Children who have been assessed as high risk often continue on an MRD monitoring program to check that their residual disease responds to the more intense chemotherapy used. The Study 8 clinical trial demonstrated that later test results are clinically valuable for high risk patients, so MRD tests are being done and reported in real time to treating oncologists for high risk patients in Study 9.
The Study 8 trial used novel combinations of intensive chemotherapy for high risk patents designed by our clinical colleagues in the Sydney Children’s Hospitals Network. This treatment doubled the numbers of high risk patients cured compared to earlier clinical trials. However, this success came at a cost of serious toxic side-effects in some patients. So in Study 9 we are using similar MRD methods and thresholds to identify high risk patients and they are being treated with a different intensive chemotherapy. The aim is to continue to improve survival of the high-risk group with less toxicity. At the other end of the spectrum, Study 9 is also trialling reduced therapy for low risk patients, to reduce the risk of side-effects.
Our collaborative studies on the Study 8 trial samples showed we can do better in identifying high risk patients by using MRD in combination with other molecular tests, particularly through testing for gene deletions and translocations associated with Ph-like disease.
Key clinical collaborators: Dr Draga Barbaric and Prof Glenn Marshall, Kids Cancer Centre, Sydney Children’s Hospital Randwick; Dr Luciano Dalla Pozza, Children’s Hospital Westmead; Dr Frank Alvaro, John Hunter Children’s Hospital; Prof Martin Schrappe i BFM, Kiel, Germany; Prof Deborah White, SAHMRI, Adelaide
A/Prof Rosemary Sutton
Since 2006, we have performed MRD testing for children with relapsed acute lymphoblastic leukaemia (ALL) at 8 children’s hospitals in Australia and New Zealand. The original ALLR3 trial also involved patients from the United Kingdom and The Netherlands. Its successor, IntReALL, is open to children with relapsed ALL from over 20 countries.
Patients are each assigned to either the high or standard risk group based on their clinical features (time to relapse, site of relapse and subtype of ALL). MRD testing is being used in the standard-risk patients (the majority) to determine for each of them whether the best option is to be treated by chemotherapy alone (in the case of patients with a very favourable MRD response after 5 weeks) or whether the patient is offered a cord blood or bone marrow transplant.
Patients in the high-risk group are all offered transplantation if a donor is available, with MRD levels monitored before and after transplantation.
The survival rates for relapsed ALL were dismal historically with only about 40 per cent of patients surviving for 5 years. The ALLR3 trial showed a remarkable improvement. In ALLR3, the three-year overall survival rates for these patients rose from an estimated 40 per cent to 61 per cent. This significant improvement was achieved mainly through substituting one of the key chemotherapy drugs. Patients given Mitoxantrone instead of Idarubicin during the first week of their therapy had significantly better results long-term. Now some patients who relapse are eligible for the IntReALL SR trial which combines the use of the best traditional chemotherapy with a trial of a new therapy, Epratuzomab. Research is particularly valuable in the context of clinical trials (since additional information is collected for these patients). The Children’s Cancer Institute’s MRD team works closely with both the Leukemia Biology and Precision Medicine Programs, as well as overseas collaborators, to investigate the nature of high risk diseases.
Key external collaborators: Professor Vaskar Saha, Christie Hospital NHS Trust Manchester (ALLR3 trial chairman); Dr Julie Irving, University of Newcastle, UK; Dr Arend von Stackelberg, Charite Hospital, Berlin and Associate Professor Tamas Revesz, Adelaide Women and Children’s Hospital (lead ANZCHOG investigator)
Funding: MRD testing for relapsed ALL patients has been supported by different funding bodies over the years including Sporting Chance Cancer Foundation (2008-2012), Cancer Council NSW and NHMRC.
A/Prof Rosemary Sutton
Since 2005, we have performed Minimal Residual Disease (MRD) testing for infants with acute lymphoblastic leukaemia (ALL) diagnosed in Australia or New Zealand. This is a small group of about 5 patients per year who are very difficult to treat, especially those with mixed-lineage leukaemia (MLL) gene rearrangements. A special form of MRD testing has been developed to measure MLL leukaemia in infants, where it is the most common marker, as well as cases of children and adults with ALL, MPAL or AML with MLL. Through collaboration with leading European laboratories, we are able to provide MLL MRD testing.
Interfant 06 is an international trial and since 2009, MRD testing has been required to assess how well the babies are responding to two different types of chemotherapy. Our team performs the tests for ANZCHOG patients. In the majority of patients (those in the medium-risk group) these tests determine if they will receive chemotherapy alone (in the case of good MRD responders) or receive chemotherapy followed by a bone marrow or cord blood transplant. The uniformity of MLL MRD testing and standardisation of interpretation across the many countries participating in the trial is ensured by the MLL MRD quality control rounds for all participating laboratories.
Key external collaborators: Professor Rob Pieters, Erasmus Medical Centre, The Netherlands (trial chairman); Prof Rolf Marschalek, Frankfurt, Germany; Dr Andrew Moore, Lady Cilento Hospital, Brisbane: and Dr Rishi Kotecha, Princess Margaret Hospital, Perth (lead ANZCHOG investigator)
A/Prof Rosemary Sutton
Several international trials showed that adolescents treated with paediatric ALL protocols have better outcomes than those treated on adult ALL protocols. Based on this success, the Australian Leukaemia and Lymphoma Group is running the ALL6 trial for patients aged 15-40 years at over 16 hospitals around Australia. This trial uses Children’s Cancer Institute MRD testing. It intensifies chemotherapy but reduces the number of transplants for adults with ALL.
A parallel research project called ‘BOMBorA – Biomarkers and MRD’ is planned.
Key external collaborators: Dr Matthew Greenwood, Royal North Shore Hospital (ALL6 trial chairman)
A/Prof Rosemary Sutton
As a part of the Study 8 trial, we showed the value of MRD levels before and after transplant in predicting successful cure. Patients with MRD persisting after transplant have a high chance of relapsing, so some interventions are being trialled to prevent relapse.
The ANZCHOG-sponsored ALLSCTped 2010 FORUM trial is an international effort to reduce the side-effects of treatment in transplant patients by replacing total body irradiation with ablative chemotherapy in some transplant patients. MRD testing before and immediately after transplant is a key part of the trial.
In addition, patients can be enrolled on an extension called ‘EMAT – Evaluation of MRD After Transplant’ that is examining the value of extended monitoring with intervention when MRD is detected.
Key external collaborators: Prof Peter Shaw, Children’s Hospital Westmead; A/Prof Tracey O’Brien, Sydney Children’s Hospital Randwick
GROUP MANAGERA/Prof Rosemary Sutton
MRD DIAGNOSTIC OFFICER
SENIOR RESEARCH ASSISTANT
SENIOR TECHNICAL OFFICER