Mass in the medial distal femoral metaphysis. Lesion is low signal on T1, high on T2 and shows enhancement. There is some surrounding bone and soft-tissue edema, cortical disruption and early soft-tissue extension of tumor.  Periosteal reaction is seen on the plain film.  A chondroid lesion is incidentally seen in the lateral proximal tibia.  

In a patient this age, an aggressive lesion with this appearance is most likely a metastasis. This woman had a known past history of breast cancer.