What are the causes of blastic and lytic lesions on bone?

Bone mets: Some bone mets stimulate an abnormal bone formation response. Osteoblasts are the cells that form bone. If this response predominates, the met looks dense(sclerotic) relative to adjacent bone, and are called osteoblastic. If instead the mets cause a bone destructive response, they are called osteolytic. Some cancers can cause both lytic or blastic lesions.