SMAD2 and osteosarcoma: Xu et al. reported that mRNAs, including those of Annexin2, Smad2, MTAP, CIP4, Cdc5L, and P27, were differentially expressed in the exosomes of patients with osteosarcoma with different chemotherapeutic responses, indicating that exosomal RNAs are reliable biomarkers for classifying osteosarcoma with different chemotherapy sensitivities [99].