2.2 Participants
This study included two groups of children: one group with solid tumors (case group) and one group of healthy children (control group). For the case group, eligible children had to meet the following criteria: 1) were diagnosed with solid tumors (e.g., sarcomas, germ-cell tumors, and neuroblastoma); 2) received at least one cycle of chemotherapy; 3) completed chemotherapy within one year; and 4) agreed to participate. Children were excluded if they did not receive any chemotherapy, could not understand and answer the questionnaires, or had a cognitive impairment, such as Down’s syndrome. Regarding the control group, healthy children who had not received antibiotics within the past 4 weeks and who had not been diagnosed with chronic or autoimmune diseases or conditions that can influence the gut microbiome profiles were included. These two groups were matched by age, sex, and race during recruitment.