How does bone metastasis cause bone changes and other problems?

Bone is the supporting framework of the body. Bones are made of a network of fibrous tissue called matrix, minerals such as calcium that attach to the matrix and give the bone its strength and hardness, and 2 main kinds of bone cells are osteoblasts and osteoclasts. Knowing a little about these 2 kinds of cells can help you understand how bone metastases grow, and how some medicines work to treat bone metastases.

The osteoblast is the cell that forms new bone, and the osteoclast is the cell that dissolves old bone.
When these cells are both working right, new bone is always forming while old bone is dissolving. This helps keep the bones strong.

Cancer cells can affect the bones by interfering with osteoblasts and osteoclasts:
  • Often, the cancer cells make substances that turn on the osteoclasts. This leads to bone being broken down without new bone being made. This weakens the bones. The holes that develop when parts of bones dissolve are called osteolytic or lytic lesions. Lytic lesions are so weak that they can cause the bone to easily break. 
  • Sometimes, the cancer cells release substances that turn on the osteoblasts. This leads to new bone being made without breaking down the old bone broken down first. This makes areas of the bones harder, a condition called sclerosis. The areas of bone where this occurs are called osteoblastic or blastic lesions. Although these blastic areas are harder, the structure of the bone is not normal and these areas actually break more easily than normal bone. 

Bone metastasis can cause other problems as well:
When cancer spreads to the bones of the spine, it can press on the spinal cord. This can cause nerve damage that may even lead to paralysis if not treated. As cancer cells damage the bones, calcium from the bones is released into the blood. This can lead to problems caused by high blood calcium levels (hypercalcemia).