A 95 year old lady with increasing pain and swelling in her thigh

X-rays of the right femur show a large permeative poorly defined lesion in the mid to distal diaphysis measuring 8 - 10 cm in total length. No periosteal reaction is appreciated. No soft tissue mass is visible on plain film. There is no calcification within the known soft tissue mass. There is a transverse sclerotic line over the distal femur. Vascular calcification is also noted on plain radiograph of the femur.
Full skeletal survey has not revealed any other sinister bony lesions but there is substantial osteoarthritis in the spine.
MRI shows a large enhancing lesion which appears to have started in the medullary space of the mid to distal diaphysis of the femur which now occupies the entire marrow space. It has extended into the soft tissue circumferentially around the femur. The lobular soft tissue mass is extensive in size measuring 13 x 8 cm in maximum dimension. The soft tissue mass extends to but does not involve the sciatic nerve. The neurovascular bundle does not appear to be involved. There is substantial permeation of the cortex of the femur.
Bone scan shows scattered uptake consistent with osteoarthritis and substantial uptake in the right distal femur for the entire length of the lesion.
CT of the chest, abdomen and pelvis were significant for two small 3mm sub-pleural nodules in the chest. These were not deemed to be indicative of metastasis. There is also sacral Paget's disease which is unchanged when compared to a previous scan 3 years prior to presentation.