When cancer cells spread to the bone, it is called bone metastasis. However, the cancer that spreads to the bone is not always the same kind that started in the patient. It may be prostate cancer, for example, that spreads to the bone, but it can also be lung or breast cancer that spreads to the bone. It is important to understand this difference when talking to patients, as it can help relieve some confusion and anxiety.
Cancer is a disease that starts when a cell begins to grow and divide faster than it should. If the cancer continues to grow, it can form small clumps of cells that are called tumors. These tumors can break away from the primary cancer and enter the bloodstream. From there, the cancer cells can travel to other parts of the body and start growing in different areas. They can also travel to the bones and form new tumors in the bone, which is called metastatic cancer or stage 4 (IV) cancer.
Bone metastases are common manifestations of distant relapse from several solid cancers, including breast and prostate. They represent a significant source of morbidity, with frequent symptoms such as pain, pathologic fracture, hypercalcemia, and spinal cord compression [1].
The primary sites for metastasis to the bone are typically red marrow-rich bones such as those found in the pelvis, ribs, and the ends of long bones. The vascularization, high rates of bone turnover, and stromal cells that produce the extracellular matrix make these sites particularly attractive for metastatic colonization and growth. The selection of these bones for metastasis also appears to be driven by their role in maintaining homeostasis in the face of metabolic stress.
Once the cancer cells have deposited in the bone, they start to resorb the bone matrix and create holes in the bones that are called lytic lesions. The metastatic tumors also trigger the production of certain molecules that promote bone resorption and further bone degradation.
Bone resorption is regulated by two proteins, osteoclasts and osteoblasts. The resorption of bone by osteoclasts is inhibited by bisphosphonates, such as denosumab and alendronate, which are also effective for the treatment of bone metastases.
If cancer has spread to the bone, doctors will want to know about all of the symptoms that the patient is experiencing. This will require a thorough imaging evaluation with X-rays or magnetic resonance imaging (MRI), which uses large magnets, radiofrequencies and a computer to produce detailed images of bones, soft tissue and ligaments without exposure to radiation. Patients with bone metastasis will usually have a history of cancer that has already spread to other parts of the body, so it is important for them to tell their doctor about any recent aches and pains. This will allow the doctor to check for signs of bone metastasis and treat them as soon as possible in order to prevent complications such as spinal cord compression.
