What percent of giant cell tumor of bone are malignant?

Answer is option 1, 5-10% the United States, giant cell tumors represent "approximately 3-5% of primary bone tumors and 20% of benign bone tumors". There are no known risk factors for giant cell tumors (1,2,3). The most common region of GCT occurrence is at the end of the long bones, especially the knee joint area. REF