High-grade surface osteosarcoma is a very rare type of bone cancer that grows on the bone’s surface. It is a type of osteosarcoma, a group of cancers in which the tumor cells make new bone. It accounts for fewer than 1% of all osteosarcomas.
“High grade” means the tumor cells look very abnormal under the microscope and the tumor can grow and spread quickly. “Surface” means the tumor starts on the outside of the bone, not in its hollow center.
Apart from where it starts, high-grade surface osteosarcoma looks and behaves like the common type of osteosarcoma that starts inside the bone. It is treated in the same way, with chemotherapy and surgery.
This article explains how high-grade surface osteosarcoma is diagnosed and what the findings in your pathology report mean.
Most osteosarcomas start inside the bone. Three types start on the surface, and the names are easy to confuse:
The type matters because each one is treated differently and has a different outlook.
High-grade surface osteosarcoma most often affects teenagers and young adults, although it can develop at any age. It is slightly more common in men than in women.
The tumor most often develops on the thigh bone (femur). The shin bone (tibia) and the upper arm bone (humerus) are the next most common sites. It usually grows on the shaft, the long middle part of the bone, or toward one end.
The cause is not known. Because the tumor is so rare, researchers haven’t studied it as closely as other osteosarcomas. Nothing you did or did not do caused it.
The most common symptoms are a lump on the arm or leg, pain, and swelling. Symptoms usually develop over a few weeks to months, faster than with slower-growing surface tumors.
The diagnosis is made by combining the imaging findings with the examination of tumor tissue under the microscope. Both are needed because the microscope shows the tumor is high grade, and the imaging shows it started on the surface.
An X-ray usually shows a mass on the surface of the bone that contains cloudy areas of new bone. The outer layer of the bone beneath the tumor may be partly worn away. An MRI or CT scan shows whether the tumor has grown into the bone’s hollow center, called the medullary cavity. In this tumor, there is little or no growth into the medullary cavity.
A biopsy removes a small sample of the tumor for examination. It should be planned at the hospital where the tumor will be treated. The path of the biopsy needle is removed along with the tumor during surgery, so its position must match the surgical plan.
Under the microscope, the tumor cells look very abnormal. They vary in size and shape, and many are dividing. The key finding is osteoid, the new, unhardened bone made directly by the tumor cells. The tumor may also make cartilage or fibrous tissue, and the amounts vary from one tumor to the next.
Pathologists and radiologists work together to separate this tumor from others that look similar:
Your report may mention a test for the MDM2 gene. Extra copies of MDM2 are found in most parosteal osteosarcomas, including those that have become high grade. A negative result supports the diagnosis of high-grade surface osteosarcoma.
Grade describes how abnormal the tumor cells look and predicts how the tumor is likely to behave. This tumor is high grade by definition. Reports may list this as “high grade,” grade 3, or grade 4, depending on the hospital’s system.
Most people receive chemotherapy before surgery. After the tumor is removed, the pathologist examines it to see how much of it is no longer alive. This is called treatment effect or tumor necrosis, and it is reported as a percentage.
Your report will describe how far the tumor has grown. Most of the tumor sits on the bone surface and grows outward into the surrounding soft tissue. The report will also say whether the tumor has grown into the outer layer of the bone or the medullary cavity. Growth into the medullary cavity, if present, is limited.
A margin is the edge of tissue the surgeon cuts when removing the tumor. The pathologist examines the bone and soft-tissue margins to see whether any tumor cells are present at the cut edge.
The pathologic stage describes the tumor size and whether it has spread. It is assigned after the tumor is removed. For tumors in the arms, legs, trunk, skull, and face, the tumor stage (pT) is:
The spine and pelvis are staged using different rules.
Osteosarcoma rarely spreads to lymph nodes, so surgeons usually do not remove them. Your report may say that the nodal stage was not assigned. When this tumor spreads, it most often goes to the lungs.
The outlook for high-grade surface osteosarcoma is similar to that of conventional osteosarcoma. Because the tumor is so rare, the available studies are small. The features that matter most are the same ones that matter for conventional osteosarcoma:
Your team can explain how these features apply to you.
A team at a center specializing in bone tumors treats high-grade surface osteosarcoma.