Bone metastases

Bone metastases are tumors that started somewhere else in the body and spread to the bone. That's why they're also called secondary bone cancer: the bone isn't where the disease began, it's where it ended up. The most common cause is carcinoma, the type of cancer that starts in the tissue covering the organs and glands, and many of these metastases come from breast, lung, or prostate cancer.

Most of the time, these cells travel through the blood. Once they arrive, they come into contact with the bone marrow stroma, the support cells of the soft tissue inside the bone. That contact sets off chemical signals that make the tumor grow and switch on osteoclasts, the cells that break down bone. Think of someone who doesn't knock down the wall with their own hands but puts a demolition crew to work instead. The result has a name: osteolysis, which means bone destruction.

A bone like that ends up like a beam eaten away from the inside. That's where the pain comes from, along with pathologic fracture, which is when a bone breaks because of the disease, even without a fall or a blow. The place these metastases show up most often is the vertebrae, the bones that make up the spine.