Migration of cells from a primary tumor to the bone micro-environment results in osteolytic, osteosclerotic or mixed lesions, causing severe, localized bone loss or growth. Bone formed in osteosclerotic lesions is abnormal and of inferior mechanical quality, resulting in pain and increased fracture risk. This project studies the progression of bone metastatic lesions using multimodal approaches including micro-CT and multiphoton imaging as well as 3D image registration in order to quantify changes in bone and collagen structure, and to study tumor and stromal cell migration to the tumor site.