Image IQ: 55-year-old Male, Swelling in Leg

55-year-old male with swelling in left leg for four months.

55-year-old male presented with chief complaints of swelling in the left leg for 4 months.

Plain radiograph of the left leg shows a large soft tissue mass in the region of the proximal femur with rings and arcs pattern of calcification and destrcution of the underlying bone.

Click on the image to enlarge.

What's your diagnosis?