Osteosarcomas show a wide variety of histologic patterns. The type of extracellular matrix produced, the degree of differentiation, the predominant cell type, and the location of the tumor (within the bone) vary from case to case. The so-called classic or conventional type makes up more than three-quarters of the cases. Based on the type of matrix produced and the cell type, conventional osteosarcomas can be further subdivided into osteoblastic (about 50% of cases), chondroblastic (25%), and fibroblastic types (25%). Slide courtesy of Piero Picci, M.D., Director, Laboratory of Experimental Oncology, Instituto Ortopedico Rizzoli, Bologna, Italy. Used with permission.