Primary bone cancer is rare. It accounts for less than 1% of all cancers diagnosed each year, making it one of the least common cancer types. Most people who hear “bone cancer” are actually dealing with cancer that started somewhere else and spread to the bone, which is a far more frequent scenario. Understanding the difference, and knowing who primary bone cancer typically affects, can help put the numbers in perspective.
Primary vs. Metastatic Bone Cancer
There are two very different ways cancer can show up in bone. Primary bone cancer starts in the bone itself. Metastatic bone cancer (also called bone metastasis) starts in another organ, like the breast, lung, or prostate, and then spreads to the skeleton. In adults, metastatic bone cancer is dramatically more common than primary bone cancer. When doctors find cancer in someone’s bones, it is far more likely to be a secondary deposit from another tumor than a cancer that originated in the bone.
This distinction matters because the two are treated differently and carry different outlooks. The rest of this article focuses on primary bone cancer, the rarer form.
The Most Common Types
Primary bone cancer isn’t a single disease. It includes several tumor types, each with its own pattern of who it affects and where it tends to grow.
- Osteosarcoma makes up roughly 45% of primary bone sarcomas. It most often appears in the arm near the shoulder or in the leg near the knee, particularly in children, adolescents, and young adults. It can occur in any bone, and older adults develop it too, though less frequently.
- Chondrosarcoma accounts for about 44% of cases. It forms in cartilage cells and typically grows slowly, most often in the pelvis, upper leg, or shoulder. It tends to affect middle-aged and older adults rather than teenagers.
- Ewing sarcoma represents roughly 6% of cases. It usually forms in the pelvis, legs, or ribs and primarily strikes children and young adults.
Several rarer types also exist. Chordomas typically form at the base of the spine or base of the skull in older adults. Giant cell tumors of bone usually develop at the ends of long bones near the knee. Osteoblastomas occur mainly in the spine. Each of these is considerably less common than the three major types listed above.
Who Gets Primary Bone Cancer
Age is the strongest predictor of which type of bone cancer someone develops. Osteosarcoma incidence peaks sharply in the 10 to 19 age range, making it one of the more common cancers in teenagers. Recent data shows that this teenage peak is consistent across decades of tracking, while an older second peak (once thought to occur after age 35) has not appeared as a reliable pattern in more recent studies. By contrast, chondrosarcoma is largely a disease of middle age and beyond, and chordomas typically appear in older adults.
Ewing sarcoma follows a pattern similar to osteosarcoma, primarily affecting children and young adults. This age split means that when a teenager is diagnosed with a bone tumor, osteosarcoma or Ewing sarcoma is the most likely culprit, while a bone tumor in a 50-year-old is more likely to be chondrosarcoma.
Known Risk Factors
For most people diagnosed with primary bone cancer, no clear cause is identified. However, a few genetic and medical factors raise the risk.
Inherited gene changes play a larger role than previously thought. Variants in the TP53 gene, linked to a hereditary condition called Li-Fraumeni syndrome, are the most frequently identified harmful gene changes in children with osteosarcoma. Research from the National Cancer Institute found these variants were more common in young osteosarcoma patients than earlier estimates suggested, meaning genetic testing may be relevant for some families.
Paget’s disease of bone, a condition where bone breaks down and regrows abnormally, can increase the risk of osteosarcoma in older adults. Prior radiation therapy to a bone (for treatment of a different cancer) is another recognized risk factor, though radiation-related bone cancers typically develop years or even decades after the original treatment.
Where Bone Cancer Typically Appears
Primary bone cancer doesn’t occur randomly throughout the skeleton. It favors specific locations depending on the tumor type. Osteosarcoma clusters around the knee and shoulder, the areas where bones grow most rapidly during adolescence. Chondrosarcoma prefers the pelvis, upper thigh bone, and shoulder. Ewing sarcoma often develops in the pelvis, legs, or ribs.
These patterns can be useful when interpreting symptoms. Persistent, unexplained bone pain near the knee in a teenager, or a slowly growing mass near the pelvis in an older adult, would warrant different levels of concern based on what type of tumor is most likely at that age and location. Swelling or a lump near the affected bone, pain that worsens at night or during activity, and occasionally a fracture through weakened bone are the most commonly reported symptoms across all types.
Survival and Outlook
Outcomes for primary bone cancer vary widely depending on the type, how early it’s caught, and whether it has spread. Localized tumors that haven’t moved beyond the bone where they started carry significantly better survival rates than those that have spread to the lungs or other bones.
Chondrosarcoma, because it tends to grow slowly, generally has a more favorable prognosis than osteosarcoma or Ewing sarcoma. Osteosarcoma and Ewing sarcoma are more aggressive, but advances in treatment over the past few decades have substantially improved outcomes, particularly for younger patients whose tumors are caught before spreading. The stage at diagnosis remains the single most important factor in long-term survival for all types of primary bone cancer.