PMC

(a–c) Osteosarcoma: (a) highly pleomorphic and bizarre tumor cells on imprint smear (MGG stain, ×100); (b) frozen section showing highly anaplastic tumor cells with pale eosinophilic osteoid formation (H&E, ×400); (c) paraffin-embedded section showing pleomorphic and polymorphic tumor cells directly laying down osteoid (H&E, ×200).

(a–c) Giant cell tumor: (a) multinucleate giant cells with nuclear morphology similar to that of background stromal cells in imprint smear (MGG stain, ×400); (b) uniformly distributed osteoclastic giant cells in a background of bland stromal cells noted in frozen section (H&E, ×100); (c) paraffin-embedded section confirming giant cell tumor (H&E, ×400).

(a–c) Chondrosarcoma: (a) hypercellular smear showing singly scattered tumor cells having moderate pleomorphism and unipolar or bipolar cytoplasmic tags; an atypical mitotic figure is also present (MGG stain, ×400); (b) fascicles of tumor cells having moderate anaplasia which are noted in frozen section (H&E, ×200); (c) paraffin-embedded section displaying a tumor arranged in short fascicles with anaplastic spindle shaped cells. Right lower corner shows malignant chondroid differentiation (H&E, ×100).

(a–c) Ewing's sarcoma: (a) imprint smear shows scattered population of malignant round tumor cells with larger cells having pale stained nuclei and smaller cells having darkly stained nuclei; cytoplasm is vacuolated (MGG stain, ×400); (b) frozen section shows sheet of small round tumor cells with occasional rosette formation (H&E, ×400); (c) malignant small round tumor cells arranged in sheets and pseudorosettes are identified in paraffin embedded section. Note mitotic figures (H&E, ×400).