The goal of this observational population-based cohort study is to investigate the clinical characteristics and outcomes of children and adolescents with primary gastrointestinal malignancies registered in the publicly available Surveillance, Epidemiology, and End Results (SEER) 17 database during 2000-2019.

The investigators aim to describe the patient and tumor characteristics, treatments, and outcomes of children and adolescents diagnosed with primary gastrointestinal malignancies, and to analyze these data for trends over time. In addition, the investigators want to explore independent prognostic factors for overall survival. Finally, the investigators want to describe subsequent primary malignancies diagnosed among patients from the study cohort, as well as to calculate their risk of developing a second primary cancer relative to the general population. Data on children (aged 0-17 years at diagnosis) and young people aged 18-24 years at diagnosis are analyzed separately. Special focus is laid on patients with primary carcinomas of the gastrointestinal tract; particularly colorectal carcinoma.

Inclusion Criteria:

• Age at primary gastrointestinal cancer diagnosis <25 years
• Diagnosis of a primary gastrointestinal malignancy as an individual's first primary malignancy

Exclusion Criteria:

• None

All patients aged 0-24 years with a diagnosis of a primary gastrointestinal malignancy as their first primary malignancy in the SEER 17 database from 2000 until (and including) 2019.

Data are publicly available through SEER under the SEER Research Data Use Agreement.

Supporting information is available on reasonable request.

When applicable, confidential information will be shared after a Data Transfer Agreement (DTA) has been signed by both parties.