UNLABELLED: Chemotherapy can alter body composition, including loss of skeletal muscle mass and density changes, which are linked to negative outcomes. This study investigates body composition changes in children and adolescents with lymphoma, focusing on the impact of chemotherapy protocols and diagnoses. A retrospective observational study included 49 lymphoma patients (ages 6-18) who underwent chemotherapy from 2017 to 2021, excluding palliative care cases. Data on disease, treatment, weight, and height were collected, and anthropometric indices, Body Mass Index by Age (BMI/A) and height by age (H/A) were calculated. Body composition was analyzed using Computed tomography (CT) at the third lumbar vertebra region (L3) with Slice-O-Matic 5.0 software, measuring skeletal muscle area (SMA), skeletal muscle density (SMD) measured in Hounsfield units (HU), total psoas muscle area (PMA), subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), and intramuscular adipose tissue (IMAT). Paired t-tests compared variables before and after treatment, and the delta of body composition parameters was stratified by chemotherapy protocols and diagnoses (Kruskal-Wallis Test), considering p <
0.05 as significant. Forty-nine patients were included (mean age 13.24 years, 49% male). After chemotherapy, there was an increase in SAT, VAT, IMAT, and SMA (p <
0.001), while SMD decreased from 41 HU to 35.27 HU (p <
0.001). The EURONET protocol and Hodgkin lymphoma were associated with increases in SAT (∆ = 78.28 cm CONCLUSIONS: Significant adipose tissue gains were observed in the EURONET protocol and Hodgkin lymphoma, highlighting the impact of chemotherapy on body composition. WHAT IS KNOWN: • Computed tomography is used to assess body composition, including muscle, adipose tissue and muscle density in adults. • Chemotherapy treatment negatively affects body composition, reducing muscle mass in adults with cancer. WHAT IS NEW: • Computed tomography can also be used to assess body composition in children and adolescents with cancer. • In pediatrics, chemotherapy can also impact body composition, with changes varying according to the administered protocol.