So confused!

I finished up treatment in October 2014. Two weeks ago I went to have a ct to recheck liver. Liver is fine but they saw "multiple tiny sclerotic lesions throughout the thoracolumbar spine that are new. The largest lesion is in the L4 vertebral body and measures 6mm." I had a bone scan last week and everything is fine and my tumor marker tests were fine. What could cause the lesions? My doctor seemed concerned and indicated that she thought that the bone scan and blood would come back normal. She really feels we need to biopsy. Could they be something other than matastesis?