Improved understanding of the long-time healthcare utilisation of childhood cancer survivors is relevant as it can be seen as a proxy for the population's morbidity.

The investigators will conduct a historic population-based matched cohort study using Danish nationwide registry data. Eligible children are children 1.0-17.9 years diagnosed with Acute lymphoblastic leukaemia (ALL) in Denmark from 1994 till 2016. The primary outcome is yearly contact rates to primary healthcare.

Acute lymphoblastic leukaemia (ALL) is the most frequent single form of cancer in children accounting for 40-45 new cases every year in Denmark. Over the past decades, advances in treatment have led to an increasing number of children who survive cancer and more than 80% of children with ALL now become long-term survivors. This means a growing population of childhood ALL survivors. In survivors, the cancer itself and treatment late-effects can lead to ongoing health care use.

Register studies of long-term survivors of childhood cancer have shown an increased risk of hospitalisation compared to the general population. It is mentioned in many of the studies that contact rates could be underestimated when looking at hospital contacts only.

The literature about non-hospital-based contacts with a doctor in childhood cancer survivors is scarce.

Inclusion Criteria:

• B-precursor ALL and T-ALL enrolled in the NOPHO ALL-92, ALL-2000 and ALL-2008 trials.
• Treated at one of the four Danish paediatric oncology departments
• Age group 1.0-14.9 for the NOPHO ALL-92 and ALL-2000 trials. Age group 1.0-17.9 for the NOPHO ALL-2008 trial.
• Completed maintenance therapy in the time period form 01.01.1997 till 31.12.2016

Exclusion Criteria:

• Children with Down syndrome

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

A reference cohort (comparison cohort) of individuals will be sampled randomly from the source population matched by age and sex and without a history of childhood cancer in the calendar year where the case was diagnosed (density sampling). For each childhood ALL-patient we will choose ten comparison subjects.