p53 gene mutations in osteosarcomas of low-grade malignancy. Alterations in tumor suppressor gene p53, localized on chromosome 17p13, are considered to play a significant role in the initiation and, to some extent, even in the progression of various malignant tumors. In this respect, investigations on conventional highly malignant osteosarcomas have shown a mutation rate of approximately 20%. However, currently, data on the mutation rate in the group of variant histology osteosarcomas of low-grade malignancy do not exist. Therefore, we investigated a panel of low malignant entities (five low malignant intramedullary osteosarcomas grade 1; one intramedullary osteosarcoma grade 2; eight parosteal osteosarcomas, including one local recurrence grades 1 and 2, and five periosteal osteosarcomas grade 2) with polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis focusing on exons 4 to 8 of the p53 gene followed by direct sequencing. Point mutations were found in one low-grade osteoblastoma-like osteosarcoma and in two periosteal osteosarcomas grade 2 (one missense, one silent, and one nonsense mutation). This mutation rate of 15.7% (3 of 19) is comparable to that determined in highly malignant osteosarcomas. Moreover, the analysis of clinical data did not show any difference in the behavior of tumors with p53 mutations compared with those without. Therefore, we suggest that alterations in p53 gene are an early event in the tumorigenesis of malignant osteoblastic tumors without impact on progression of these tumors.