Figure 1

Osteosarcoma arising from the left distal femur in a 15-year-old boy. (A,B) Before chemotherapy. (A) Magnetic resonance imaging (MRI) scan of the tumor obtained before neoadjuvant chemotherapy; arrows show lesions in longest diameter. (B) Tumor cells (hematoxylin and eosin (H&E), original magnification × 40). (C,D) After chemotherapy. (C) MRI scan of the same tumor after chemotherapy showed that there was no tumor extension into the epiphysis. Extensive calcification and the significantly reduced lesion (arrows, the sum of the longest diameter ≥30% reduction) indicated a good response to therapy. (D) Significant tumor cell degeneration and necrosis (H&E, original magnification × 40).