Objective: Osteosarcoma of the bone accounts for approximately 20% of all primary malignant bone tumors. Most cases (75-85%) are high-grade osteosarcomas. We aimed to introduce low-grade osteosarcomas that we found by retrospectively scanning our archives because of the diagnostic difficulties, rarity and different therapeutic approach required.

Material and Method: We found 156 osteosarcoma cases in the archives of the Department of Pathology of Istanbul University, Cerrahpaşa Faculty of Medicine covering the period 2000 to 2010. These cases included 141 high-grade and 15 low-grade osteosarcomas.

Results: Low-grade osteosarcomas made up 10.4% of all osteosarcomas. Age and sex distribution were 19 to 54 (median 33.6) with 9 females and 6 males. Most cases were located in the distal femur while others were in the proximal tibia, the left wrist, the distal tibia and the right knee. The tumors were generally made up of relatively well-formed trabeculae of woven bone surrounded by a moderately cellular spindle cell proliferation entangled in collagen fibers. Thirteen cases were reported as parosteal osteosarcoma, one as intramedullary well-differentiated osteosarcoma, and one as low-grade osteosarcoma metastasis in the lung.

Conclusion: Low-grade osteosarcomas account for approximately 3-5% of all osteosarcomas. They are more commonly seen in women and 9 cases out of 6 were female in our series. The average age was 33.6 (19-54). The distal femur was the most common localization as is typical in osteosarcomas. In contrast to high-grade lesions, surgery will be sufficient in low-grade osteosarcomas. The survival rate ranges from 90% to 100%. Differentiating low-grade osteosarcomas from high-grade osteosarcomas and benign lesions and using a multidisiplinary approach for the diagnosis, treatment and follow-up periods are of vital importance.