IDH1 and osteosarcoma: Although we used subcloning method to confirm that OS12 possesses IDH2-R172S mutation (Fig. 1), MsMab-1 mAb did not stain OS12 in immunohistochemistry (Table 1), probably because (1) the sensitivity of MsMab-1 is not sufficiently high to detect all IDH2-R172S proteins in immunohistochemistry, (2) the expression of IDH2-R172S protein is heterogeneous in osteosarcoma tissues, as shown in Figures 3 and 4, or (3) IDH-R172S protein might be degraded in a paraffin section of OS12 because of fixation by formalin.