3.1 Characteristics of participants
Forty-nine children were enrolled including 27 cancer cases and 22 healthy controls (Table 1) . The cancer group included 13 boys and 14 girls, with a mean age of 14.4 years. The control group consisted of 9 boys and 13 girls, with a mean age of 12.1 years. No significant differences were found between the two study groups in age (P = 0.053), gender (P = 0.774), race (P = 0.172), and BMI (P = 0.346).