The pilot study collects the experience of previously successful treatment of infants, children and young adults, with ALL from a number of well-renowned study groups into a new platform protocol, which is both a comprehensive system for stratification and treatment of ALL in this age-group as well as the basis for several randomised trials included in the study-design.

The pilot study is implemented as a master protocol without study specific interventions, thus as an observational study. The pilot study is for countries/study-groups who intend to join ALLTogether1 (including experimental interventions). For these countries the pilot study is crucial to optimise diagnostics, registration systems, collaborations with vendors, logistics and data-checks before starting the main study.

The study only includes "standard of care" treatment included in the master protocol.

The aims of the ALLTogether study are to improve survival and quality of survival for children and young adults with ALL. ALL in young people has excellent outcome with >90% survival in children and about 75% in young adults. However, patients still die of disease - after relapse as a result of under-treatment.

Furthermore, a considerable fraction of younger patients are over-treated: All patients risk treatment-related death and some suffer long-term side-effects or secondary cancer. The rates of death from disease and death from therapy are almost the same for children. To show improvement with such good survival, large populations are needed.

Study groups from the five Nordic countries, Estonia and Lithuania (NOPHO), the UK (UKALL), the Netherlands (DCOG), Germany (COALL), Belgium (BSPHO), Ireland (PHOAI), Portugal (SHOP) and France (SFCE) have designed a common treatment protocol as new standard of care for children and young adults with ALL. The risk-stratification is based on a novel, personalised algorithm using clinical characteristics, genetic changes in the leukaemia and response to therapy.

The protocol will, based on a personalised risk-approach, define a platform for diagnosis and treatment onto which randomized as well as non-randomised interventions and translational studies can be added. This platform can also be used by countries joining the collaboration at a later date to prepare for full participation.

High-risk B-lineage patients may be stratified to Chimeric Antigen Receptor T-cell (CAR-T) therapy as an alternative to high-risk blocks and stem-cell transplant to reduce the side-effects.

Translational and other therapy-related research will be promoted by the common master protocol.

Inclusion Criteria:

• Patients newly diagnosed with T-lymphoblastic (T-cell) or B-lymphoblastic precursor (BCP) leukaemia (ALL) according to the WHO-classification of Tumours of Haematopoietic and Lymphoid Tissues (Revised 4th edition 2017) and with a diagnosis confirmed by an accredited laboratory at a participating paediatric oncology or adult haematology centre.
• Age 0 - < 46 years (one day before 46th birthday) at the time of diagnosis, with the exception of infants with KMT2A-r BCP ALL (see exclusion criteria below).
• Patients with surface immunoglobulin negative (sIG-) BCP-ALL and an IG::MYC rearrangement, unless they have a concurrent BCL2/6 rearrangement. T-ALL patients with MYC translocations.
• Informed consent signed by the patient and/or parents/legal guardians according to country-specific age related guidelines
• The ALL diagnosis should be confirmed by an accredited laboratory at a participating paediatric oncology or adult haematology centre.
• The patient should be diagnosed and treated at a participating paediatric oncology or adult haematology centre in the participating countries.
• The patient should be a resident in one of the participating countries on a permanent basis or should intend to settle in a participating country, for instance by an application for asylum. Patients who are visiting the country as tourists should not be included. However, returning expatriots and patients who intend to stay at least for the duration of the treatment with primary diagnosis abroad may be included if no treatment has been administered and the diagnostic procedures are repeated at a participating centre.
• All women of childbearing potential (WOCBP) have to have a negative pregnancy test within 2 weeks prior to the start of treatment.

Exclusion Criteria:

• Age < 365 days and KMT2A-rearranged (KMT2A-r) BCP-ALL (documented presence of a KMT2A-split by FISH and/or a KMT2A fusion transcript). These patients will be transferred to an appropriate trial for infant KMT2A-r BCP-ALL, if available.
• Age >45 years at diagnosis.
• Patients with a previous malignant diagnosis (ALL as a second malignant neoplasm - SMN).
• Relapse of ALL.
• Patients with mature B-ALL (as defined by surface IG positivity) or any patients with IG::MYC and a concurrent BCL2/6 rearrangement.
• Patients with Ph-positive ALL (documented presence of t(9;22)(q34;q11) and/or of the BCR::ABL1 fusion transcript). These patients will be transferred to an appropriate trial for t(9;22) if available.
• Previously known ALL prone syndromes (e.g. Li-Fraumeni syndrome, germline ETV6 mutation), except for Down syndrome. Exploration for such ALL prone syndromes is not mandatory and patients in whom genetic work-up reveals a new germ-line mutation (index-cases) will remain in the study.
• Treatment with systemic corticosteroids corresponding to (>10mg prednisolone/m2/day) for more than one week and/or other chemotherapeutic agents in a 4-week interval prior to diagnosis (pre-treatment).
• Pre-existing contraindications to any treatment according to the ALLTogether protocol (constitutional or acquired disease prior to the diagnosis of ALL preventing adequate treatment).
• Any other disease or condition, as determined by the investigator, which could interfere with the participation in the study according to the study protocol, or with the ability of the patients to cooperate and comply with the study procedures.
• Women of childbearing potential who are pregnant at the time of diagnosis.
• Women of childbearing potential and fertile men who are sexually active and are unwilling to use adequate contraception during therapy. Efficient birth control is required, see section 18.9.
• Female patients, who are breast-feeding.
• Essential data missing from the registration of characteristics at diagnosis (in consultation with the protocol chair).

Participants 0-45 years with newly diagnosed acute lymphoblastic leukaemia. The protocol has no gender-bias. The total estimated recruitment in the pilot study is 500 participants.

Individual participant data will be entered into the study database. The data will be used to inform the coming main study regarding safety and overall outcomes of the master protocol. As such, these outcomes may be published in the context of a comparison with the ALLTogether1 protocol (the master protocol including experimental interventions, NCT 04307576, or compared with legacy protocols of the participating study-groups, The data of the pilot protocol will be shared according to the same principles as ALLTogether1 data.