Over the past decades, advances in treatment have led to an increasing number of children who survive cancer, resulting in a growing population of childhood cancer survivors. After end of cancer treatment on common protocols survivors are enrolled in non-harmonized follow-up programs with frequent visits and blood samples. However, the evidence for the value of these follow-up programs with respect to the effect on detecting relapse and the effects on overall survival is scarce.

The aim of the study is to give a comprehensive description of the detection mode of relapsed acute lymphoblastic leukaemia (ALL), including symptoms and blood test results. Further, we aim to evaluate if the mode of detection affects survival.

Investigators have identified a cohort of children with B-precursor ALL and T-ALL enrolled in the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL-92, ALL-2000 and ALL-2008 trials and experienced a relapse or an SMN as the first event after cessation of maintenance therapy (368 patients). From medical charts and blood test results it will be decided whether the relapse/SMN was diagnosed at a routine visit (including routine blood tests) or if the relapse was diagnosed because of symptoms at a non-scheduled visit or blood test.

As the NOPHO database probably is one of the most complete databases globally, it is an advantage to perform this study as a NOPHO study.

Results of this population based relapse study will provide an evidence-based background for planning optimal and relevant follow-up programs for children after therapy of ALL treated according to contemporary Nordic ALL protocols.

The study is important and relevant in the light of today's high ALL cure rates and a need for optimal follow-up programs after cessation of ALL treatment and possible prediction of relapse.

The timing of the project is an increased focus on the clinical relevance of routine clinical follow-up of patients treated for cancer.

Inclusion Criteria:

• diagnosed with pre-B or T-cell ALL in the Nordic countries (Denmark, Sweden, Norway, Finland or Iceland)
• included in the NOPHO ALL-92, ALL-2000 or ALL-2008 trials
• treated in a Paediatric Department
• developing a relapse/SMN after cessation of maintenance therapy before 31st of December 2016

Exclusion Criteria:

• hematopoietic stem cell transplantation in first complete remission

The study population will be identified in the Nordic Society of Paediatric Haematology and Oncology ALL database.