Chondroblastic osteosarcoma is a type of bone cancer. It is one form of osteosarcoma, the most common bone cancer.
All osteosarcomas are made of cancer cells that produce bone. In chondroblastic osteosarcoma, much of the tumor is made of cartilage instead, the firm, smooth tissue found in joints and in the ear. The cancer cells also make that cartilage. The word chondroblastic refers to this cartilage.
Chondroblastic osteosarcoma is one of the most common forms of osteosarcoma, making up roughly a quarter of cases. It behaves and is treated like other high-grade osteosarcomas, with one important exception for jaw tumors, described below.
This article explains how chondroblastic osteosarcoma is diagnosed and what the findings in your pathology report mean.
Like other osteosarcomas, chondroblastic osteosarcoma most often affects teenagers and young adults, during the years when bones grow fastest. It usually develops in the long bones of the legs and arms, most often near the knee or the shoulder.
Chondroblastic osteosarcoma is also the most common form of osteosarcoma in the jaw. Jaw tumors usually develop in adults in their 30s and 40s, which is later than osteosarcoma elsewhere.
For most people, no cause is found. Osteosarcoma is not caused by injury, although an injury sometimes draws attention to a tumor that was already there.
A small number of cases develop in people with an inherited condition that raises the risk of cancer. These include Li-Fraumeni syndrome and hereditary retinoblastoma, as well as rarer conditions such as Rothmund-Thomson syndrome. Your team may discuss genetic assessment if you have a family history of cancer or if the tumor develops at an unusual age.
In older adults, osteosarcoma can develop in a bone affected by Paget disease of bone, or in an area treated with radiation therapy years earlier.
The most common symptom is bone pain that gets worse over weeks or months. The pain is often worse at night and may not settle with rest.
Swelling or a lump may develop over the affected bone. Because the tumor weakens the bone, it can break with little or no force, which is called a pathologic fracture. A tumor in the jaw may cause swelling, loose teeth, or numbness of the lip or chin.
X-rays and MRI usually show a bone tumor. The diagnosis is confirmed with a biopsy, in which a small sample of the tumor is removed and examined by a pathologist.
The biopsy should be done at the center that will perform the final surgery. The track left by the biopsy needle has to be removed along with the tumor later, so its position affects the operation.
Under the microscope, the pathologist looks for one key feature: cancer cells producing immature bone, called osteoid. Finding tumor-made bone is what makes the diagnosis osteosarcoma, even when cartilage makes up most of the tumor.
Because chondroblastic osteosarcoma contains so much cartilage, it can look like a chondrosarcoma, a different bone cancer made only of cartilage. Distinguishing the two is one of the pathologist’s most important tasks because they are treated very differently.
Osteosarcoma is treated with chemotherapy as well as surgery. Chondrosarcoma is treated mainly with surgery, because it responds poorly to chemotherapy. Calling an osteosarcoma a chondrosarcoma could mean missing treatment that improves the chance of cure.
A small biopsy may contain only cartilage, without the tumor-made bone that confirms osteosarcoma. The pathologist therefore considers the patient’s age, the location of the tumor, and the imaging along with the biopsy. A stain called SATB2, which highlights bone-forming cells, can also help.
The grade describes how abnormal the cancer cells look and how quickly the tumor is likely to grow and spread. Chondroblastic osteosarcoma is always a high-grade tumor.
Your report may state that the tumor is high grade, or it may not give a grade at all, because the diagnosis already implies it. This is different from a few rarer forms of osteosarcoma that are low grade.
Most people with chondroblastic osteosarcoma receive chemotherapy before surgery. When the tumor is removed, the pathologist examines it closely to see how much of it was killed by the chemotherapy. This is reported as a percentage of tumor necrosis, meaning the percentage of dead tumor.
A result of 90% or more is called a good response, and it is linked to a better outlook. A result below 90% is called a poor response.
A poor response does not mean treatment has failed. Many people with a poor response are still cured, and your team may adjust treatment after surgery based on this result. The cartilage in chondroblastic osteosarcoma may respond to chemotherapy more slowly than other parts of the tumor. Some studies suggest that this subtype shows a lower percentage of necrosis without a matching effect on survival.
Your report may describe whether the tumor has broken through the outer surface of the bone into the surrounding muscle or other soft tissue. This is called extraosseous extension, and it is common in osteosarcoma.
The report may also note whether the tumor has grown into a nearby joint or into an adjacent bone. In the spine and pelvis, which are made of several connected bones, spread from one bone to another raises the stage.
A margin is the edge of tissue cut by the surgeon. Your report will list each margin and whether the tumor reaches it. Margins for a bone tumor usually include the cut ends of the bone, the surrounding soft tissue, and any large blood vessels or nerves removed.
Your report may state whether cancer cells were seen inside small blood vessels or around nerves. Both findings are uncommon in osteosarcoma, and the report will often say that neither was identified.
Bone cancers are staged using the TNM system from the American Joint Committee on Cancer (AJCC), 8th edition. The tumor stage, called pT, depends on which bone is involved, so the same number does not mean the same thing in every bone:
Spread to distant sites matters most. The lungs are by far the most common place for osteosarcoma to travel, which is why a CT scan of the chest is part of the assessment at diagnosis.
The outlook for chondroblastic osteosarcoma is similar to that of other high-grade osteosarcomas. It depends most on whether the tumor has spread, how completely it can be removed, and how well it responds to chemotherapy.
Tumors of the spine and pelvis, large tumors, and positive margins are linked to a less favorable outcome. These figures describe groups of people and cannot predict what will happen to one person.
Chondroblastic osteosarcoma is managed by a team at a center that treats bone sarcomas regularly. The team usually includes an orthopedic oncologist, a medical or pediatric oncologist, a radiologist, and a pathologist.
Radiation therapy is used mainly when surgery is not possible, because osteosarcoma does not respond well to it.