A research team from Taiwan reported an unusual case of pelvic-abdominal inflammatory myofibroblastic tumor (IMT) with malignant transformation in a 14-year-old boy presenting with abdominal pain and 9 kg body weight loss in one month. This is the largest documented case of IMT in a pediatric patient and the first report of IMT with malignant transformation originating from the pelvic extraperitoneal space.