Talk to General Physician on Suspected Malignancy

My 14 years old c/o lower backache radiating to left lower quadrant and left leg for last 7 months not settling with analgesics, denies low grade fever, night sweats or weight loss subsequently got mri LS spine although inconclusive but shows 13cm mass arising from left iliac bone. Routine bloods mildly elevated esr 25, normal wcc, crp. CT thorax abd and pelvis done yesterday. Would appreciate your opinion regarding further management