The peak incidence of giant cell tumor is seen in the 3rd decade of life with a female predominance. The most commonly involved locations include ends (epiphyses) of long bones - distal femur, proximal tibia and distal radius. Roughly half of all cases occur around the knee joint. Sarcum is another common location. Slide courtesy of Piero Picci, M.D., Director, Laboratory of Experimental Oncology, Instituto Ortopedico Rizzoli, Bologna, Italy. Used with permission.