A bone tumor is an abnormal mass of tissue that forms when cells inside or on the surface of a bone grow in an uncontrolled way. These growths can be benign (noncancerous) or malignant (cancerous), and the distinction between the two shapes everything about how they behave, how they’re treated, and what they mean for your long-term health. Primary bone cancers are rare, with an estimated 3,770 new cases projected in the United States for 2025, but benign bone tumors are far more common and often discovered by accident on an X-ray taken for something else.
How Bone Tumors Form
Healthy bone is constantly remodeling itself. Specialized cells called osteoblasts build new bone tissue while osteoclasts break down old bone, and the two processes stay in balance. A bone tumor disrupts that balance. In many cases, the tumor cells send out chemical signals that ramp up bone destruction while slowing down or distorting new bone formation. The result is a growing mass that can weaken the surrounding bone, sometimes creating a self-sustaining cycle: the tumor stimulates bone-destroying cells, which carve out space that allows the tumor to expand further.
Bone tumors can originate from different cell types. Some arise from bone-forming cells, others from cartilage cells, and still others from connective tissue or blood vessel cells within the bone. The cell of origin largely determines whether the tumor is benign or malignant and how it’s classified.
Benign Bone Tumors
Most bone tumors are benign. They don’t spread to other parts of the body, and many never need treatment. The most common types include osteochondroma, osteoid osteoma, enchondroma, giant cell tumor, and fibrous dysplasia.
Osteochondroma is the single most common benign bone tumor, making up roughly 50% of all benign bone tumors and about 15% of all primary skeletal growths. These cartilage-capped outgrowths typically appear during adolescence near the growth plates of long bones, especially around the knee. Most cause no symptoms and are found incidentally.
Osteoid osteoma accounts for about 12% of benign bone tumors and most often shows up in the femur or tibia during the teenage years, affecting boys two to four times more than girls. It produces a distinctive pain pattern: a deep, aching bone pain that tends to worsen at night and reliably improves within 30 minutes of taking an over-the-counter anti-inflammatory like ibuprofen. The tumor itself is small, typically less than 1.5 centimeters across, with a central core called a nidus that produces pain-triggering chemicals.
Enchondroma is a cartilage tumor that can develop in almost any bone but has a particular tendency to appear in the small bones of the hands. It’s the most common tumor found in the hand. Enchondromas are usually painless and discovered incidentally, though they can occasionally weaken the bone enough to cause a fracture.
Giant cell tumor tends to appear at the ends of long bones, most commonly around the knee in the lower femur or upper tibia. Despite being classified as benign, it behaves aggressively, causing significant bone destruction. In rare cases it can recur after treatment or, uncommonly, spread to the lungs.
Primary Malignant Bone Tumors
Cancerous bone tumors that originate in the bone itself are called primary bone cancers. They are uncommon but serious. The three main types are osteosarcoma, chondrosarcoma, and Ewing sarcoma.
Osteosarcoma is the most common primary bone cancer, representing about 21% of malignant bone tumors. It has two peak age groups: teenagers and young adults (ages 10 to 20) and older adults (ages 50 to 70). It typically affects the long bones of the legs or arms, especially around the knee. The five-year survival rate for localized osteosarcoma is about 68%, but drops to under 30% when the cancer has spread to distant sites.
Chondrosarcoma arises from cartilage cells and accounts for roughly 20% of malignant bone tumors. Unlike osteosarcoma, it’s primarily a disease of middle-aged and older adults, typically appearing between ages 30 and 60. It tends to grow more slowly than osteosarcoma, though high-grade forms can be aggressive.
Ewing sarcoma makes up about 5% of malignant bone tumors and primarily affects children, teenagers, and young adults between ages 10 and 30. It can develop in any bone but commonly involves the pelvis, femur, and ribs.
Secondary Bone Tumors From Other Cancers
Far more common than primary bone cancer are metastatic bone tumors, which are cancers that started somewhere else in the body and spread to the bone. The cancers most likely to do this are prostate, lung, breast, kidney, and thyroid cancers. Prostate cancer carries the highest risk, with 18% to 29% of cases eventually spreading to bone.
Where the cancer ends up in the skeleton often depends on where it started. Breast and lung cancers tend to spread to the thoracic spine (mid-back) and ribs because of how blood drains from the chest. Prostate cancer usually targets the lower spine and pelvis. Overall, the spine is the most frequently affected site, followed by the femur, pelvis, ribs, sternum, upper arm bone, and skull.
Symptoms to Recognize
The most common symptom of a bone tumor is pain at the site of the growth. With benign tumors like osteoid osteoma, the pain often has a predictable nighttime pattern. With malignant tumors, the pain typically starts as intermittent and gradually becomes constant over weeks or months. In teenagers, bone cancer pain is sometimes mistaken for growing pains, which can delay diagnosis.
Other signs include visible swelling or a firm lump near a bone, and in some cases, a fracture that occurs with minimal or no trauma. A bone weakened by a tumor can snap during normal activity, a so-called pathological fracture, and this is sometimes the first indication that anything is wrong.
Who Gets Bone Tumors
Bone tumors can develop at any age, but the pattern depends on the type. Primary bone cancers are disproportionately a disease of the young: about 23% of new cases occur in people under 20, and another 15% in those aged 20 to 34. There’s a second, smaller peak in adults over 55, accounting for about 43% of cases. Benign bone tumors like osteochondroma are most commonly discovered during adolescence, when bones are growing rapidly.
How Bone Tumors Are Diagnosed
The diagnostic process almost always starts with a standard X-ray, which remains the best initial imaging tool for bone lesions. A skilled radiologist can often distinguish aggressive tumors from nonaggressive ones just by looking at how the bone’s edges appear, whether there’s a pattern of destruction, and how the outer layer of bone is reacting to the growth. Some benign tumors have such a characteristic look on X-ray that no further workup is needed.
When the X-ray raises concern, MRI provides a more detailed picture. It’s especially useful for seeing how far a tumor extends into the bone marrow, whether it’s pressing on nearby nerves or blood vessels, and whether it involves a joint. CT scans may also be used, particularly when the bone detail on X-ray needs clarification.
If there’s any suspicion of malignancy, a biopsy is performed to examine tumor cells under a microscope. This usually involves inserting a needle through the skin and into the tumor to extract a small core of tissue. Larger needles that preserve the tissue’s structure are preferred over fine-needle techniques because they give pathologists more to work with and produce more reliable results. For tumors that are very dense or surrounded by thick bone, a two-part coaxial needle system allows doctors to collect multiple samples through a single entry point.
Treatment Approaches
Treatment depends entirely on whether the tumor is benign or malignant, how aggressive it is, and where it’s located.
Many benign bone tumors require no treatment at all. If a tumor is small, painless, and not weakening the bone, your doctor may simply monitor it with periodic imaging. Osteoid osteomas, for example, can sometimes be treated with a minimally invasive procedure that uses heat to destroy the small central core of the tumor. Larger or more aggressive benign tumors may need surgical removal.
For malignant bone tumors, surgery is the primary treatment. The goal is to remove the entire tumor along with a margin of healthy tissue. In most cases, surgeons can perform limb-sparing surgery, removing the cancerous section of bone and reconstructing it with a bone graft from another part of the body or with metal and plastic implants. Amputation is uncommon today but may be necessary when the tumor is very large or located in a position that makes reconstruction impossible. If an amputation is performed, a prosthetic limb is an option.
Chemotherapy plays a major role in treating osteosarcoma and Ewing sarcoma, typically given both before surgery (to shrink the tumor) and after (to target any remaining cancer cells). Chondrosarcoma, on the other hand, generally doesn’t respond well to chemotherapy, making complete surgical removal especially critical. Radiation therapy may be used for Ewing sarcoma or for tumors in locations where surgery is difficult, such as the spine or pelvis.
Common Locations in the Skeleton
Bone tumors have strong preferences for certain parts of the skeleton. The long bones of the legs, particularly the femur and tibia, are the most common sites overall. Many tumors favor specific zones within a bone. Osteosarcoma and osteochondroma tend to develop in the metaphysis, the flared section near the ends of long bones where growth occurs. Giant cell tumors and chondroblastoma prefer the epiphysis, the very tip of the bone near the joint surface.
Beyond long bones, the pelvis, ribs, and spine are also common locations, depending on the tumor type. Fibrous dysplasia frequently affects the ribs. Ewing sarcoma has a notable tendency to involve the pelvis. And metastatic bone tumors, as noted, overwhelmingly favor the spine.