Bone metastasis

Bone metastases, or metastatic bone disease, is a class of cancer metastases that results from primary tumor invasion to bone. Bone-originating primary tumors such as osteosarcoma, chondrosarcoma, and Ewing's sarcoma are rare. Unlike hematological malignancies that originate in the blood and form non-solid tumors, bone metastases generally arise from epithelial tumors and form a solid mass inside the bone. Bone metastases cause severe pain, characterized by a dull, constant ache with periodic spikes of incident pain.

Bone is the third most common location for metastasis, after the lung and liver. While any type of cancer is capable of forming metastatic tumors within bone, the microenvironment of the marrow tends to favor particular types of cancer, including prostate, breast, and lung cancers. Particularly in prostate cancer, bone metastases tend to be the only site of metastasis. The most common sites of bone metastases are the spine, pelvis, ribs, skull, and proximal femur.

Common primary tumors

Under normal conditions, bone undergoes a continuous remodeling through osteoclast-mediated bone resorption and osteoblast-mediated bone deposition. These processes are normally tightly regulated within bone to maintain bone structure and calcium homeostasis in the body. Disregulation of these processes by tumor cells leads to either osteoblastic or osteolytic phenotypes, reflective of the underlying mechanism of development. Typically, osteolytic metastases are more aggressive than osteoblastic metastases, which have a slower course. Regardless of the phenotype, though, bone metastases show osteoclast proliferation and hypertrophy.

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