Complete fatty replacement of lytic bone metastases following treatment. A case report, assessing response to treatment of bone metastases on CT imaging

Bone is the most common site for breast cancer metastases, occurring in up to 70% of patients, who have metastatic disease. The treatment of advanced breast cancer with bony metastases has significant health and economic implications including the costs of imaging, systemic therapy, and hospital admission. Therefore, accurate interpretation of response to therapy in bone metastases on post-treatment computed tomography (CT) imaging is an essential role of the radiologist in daily practice. It is well recognized that lytic metastases become sclerotic in response to treatment, but it is less appreciated that lytic metastases can become fatty in response to treatment as in this index case. We present a case of post-treatment lytic bone metastases demonstrating an unusual finding of complete fatty replacement within the lesions indicating a response to treatment.