Osteopontin levels have been shown to correlate with direct O2 measurements, predicting disease progression and response to treatment in some adult cancers.29,30 The potential use of osteopontin as a biomarker has been demonstrated in childhood cancers, such as acute lymphoblastic leukaemia (ALL), malignant gliomas31 and osteosarcoma,32 although further investigation is required for clinical use. This evidence concerns the gene SPP1 and osteosarcoma.