Telangiectatic Osteosarcoma: Understanding Your Pathology Report

Section Editor: Bibianna Purgina, MD FRCPC
October 7, 2026

Telangiectatic osteosarcoma is a rare type of osteosarcoma, a bone cancer made of bone-producing cells. It makes up fewer than 4 in 100 osteosarcomas.

Telangiectatic describes widened blood vessels. Most of this tumor is made of large spaces filled with blood, separated by thin walls that contain the cancer cells. This gives the tumor a sponge-like appearance on imaging and under the microscope.

Telangiectatic osteosarcoma is a high-grade cancer. It is treated the same way as other high-grade osteosarcomas, and with modern treatment its outlook is similar.

This article explains how telangiectatic osteosarcoma is diagnosed and what your pathology report findings mean.

Who gets telangiectatic osteosarcoma?

Telangiectatic osteosarcoma most often affects teenagers and young adults, during the years when bones grow fastest. It is about twice as common in males.

It usually develops near the ends of the long bones of the legs and arms. The most common locations are the lower end of the thigh bone and the upper end of the shin bone, near the knee. The upper end of the arm bone, near the shoulder, is also a common site.

What causes telangiectatic osteosarcoma?

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 osteosarcomas develop in people with an inherited condition that raises the risk of cancer, such as Li-Fraumeni syndrome or hereditary retinoblastoma. Your team may discuss genetic assessment if you have a family history of cancer.

What are the symptoms of telangiectatic osteosarcoma?

The most common symptoms are pain and swelling over the affected bone, often building over a few months. The pain may be worse at night.

Because the tumor destroys a great deal of bone, it weakens the bone more than most osteosarcomas. In about a quarter to a third of people, the bone breaks with little or no force. This is called a pathologic fracture, and it is often how the tumor is first discovered.

Why can telangiectatic osteosarcoma be mistaken for an aneurysmal bone cyst?

An aneurysmal bone cyst is a noncancerous bone tumor made of blood-filled spaces. It develops in the same age group and often in the same bones. The two can look very similar on X-ray and MRI, and sometimes under the microscope.

This is the most important challenge with this diagnosis. Telling the two apart matters because an aneurysmal bone cyst is usually treated by scraping it out of the bone. Telangiectatic osteosarcoma needs chemotherapy and a larger operation. A telangiectatic osteosarcoma mistaken for an aneurysmal bone cyst can be undertreated.

Several clues help your team separate them:

Imaging. Both tumors can show fluid levels on MRI, where blood separates into layers. An aneurysmal bone cyst is usually filled with these layered spaces and has a well-defined edge. Telangiectatic osteosarcoma more often has solid areas, thick walls between the spaces, and a poorly defined edge where it grows into the surrounding bone.
The cells in the walls. In an aneurysmal bone cyst, the cells lining the spaces look normal. In telangiectatic osteosarcoma, the cells in the walls look clearly abnormal.
Molecular testing. Most aneurysmal bone cysts have a change in a gene called USP6. Telangiectatic osteosarcoma does not. A test for this change can help when the microscope findings are uncertain.

How is the diagnosis made?

X-rays, CT, and MRI show a tumor that has destroyed bone, often with blood-filled spaces. The diagnosis is confirmed with a biopsy, in which a 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.

Because so much of this tumor is blood, a biopsy may contain mostly blood and very few tumor cells. The biopsy targets the solid areas and walls seen on imaging, where the cancer cells are found. Sometimes a second biopsy is needed.

Under the microscope, the pathologist sees large blood-filled spaces separated by thin walls. The walls contain highly abnormal cells, many of which are dividing. These cells make small amounts of immature bone, called osteoid. Finding tumor-made bone confirms that the tumor is an osteosarcoma, even when only a little is present.

Grade

Telangiectatic 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.

Treatment effect

Most people with telangiectatic osteosarcoma receive chemotherapy before surgery. When the tumor is removed, the pathologist examines it 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 a result below 90% is called a poor response. For telangiectatic osteosarcoma, chemotherapy response is the strongest predictor of outlook. This type often responds well, and some studies show it responds better than other osteosarcomas.

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.

Tumor extension

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.

Margins

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.

Negative margin. No cancer cells are seen at the cut edge. The report may also give the distance between the tumor and the closest margin.
Positive margin. Cancer cells reach the cut edge so that some tumor may remain. This raises the chance that the cancer will come back in the same place, and further surgery or other treatment may be considered.

A pathologic fracture can spread tumor cells into the surrounding tissue. The surgeon considers this when planning how much tissue to remove.

Stage

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:

Arms, legs, trunk, skull, and face. The stage depends mainly on size. A tumor 8 cm or smaller is pT1, and a tumor larger than 8 cm is pT2. Separate tumor deposits within the same bone are pT3.
Spine and pelvis. These bones have their own staging rules, based on how many bone segments are involved and whether the tumor extends beyond the bone.
Lymph nodes. Osteosarcoma spreads through the bloodstream rather than the lymphatic system, so lymph nodes are rarely involved and are often not removed. When no nodes are examined, the report may say the nodal stage was not assigned.

Spread to distant sites matters most. The lungs are the most common place for osteosarcoma to travel, followed by other bones. This is why a CT scan of the chest is part of the assessment at diagnosis.

What is the prognosis?

Telangiectatic osteosarcoma was once thought to have a poor outlook. With modern chemotherapy and surgery, its outlook is similar to that of other high-grade osteosarcomas.

Overall. In the largest single-center series of 87 people, about 64% were alive five years after diagnosis and about 61% at 10 years. Most survivors are cured.
Response to chemotherapy. This is the strongest predictor of outcome. People whose tumor is 90% or more dead at surgery do best.
Spread at diagnosis. Cancer that has already spread to the lungs or other bones is harder to treat.
Pathologic fracture. In the large series, a fracture at diagnosis did not on its own lead to a worse outcome.
Age. Children and teenagers tend to do better than adults.

These figures describe groups of people and cannot predict what will happen to one person.

What happens after the diagnosis?

A team at a center that regularly treats bone sarcomas manages telangiectatic osteosarcoma. The team usually includes an orthopedic oncologist, a medical or pediatric oncologist, a radiologist, and a pathologist.

Chemotherapy before surgery. Treatment usually begins with several cycles of chemotherapy, the same as for other high-grade osteosarcomas.
Surgery. The tumor is removed with a rim of normal tissue in a resection. Limb-sparing surgery, in which the bone is replaced with a metal implant or a bone graft, is possible for most people, including many who had a fracture.
Chemotherapy after surgery. Further chemotherapy usually follows, and the treatment effect may guide it.
Follow-up. Follow-up continues for years, with imaging of the original site and of the chest.

Radiation therapy is used mainly when surgery is not possible, because osteosarcoma does not respond well to it.

Questions to ask your doctor

How was my tumor told apart from an aneurysmal bone cyst?
Was USP6 testing done, and was it needed?
What percentage of the tumor was dead after chemotherapy?
Were all the margins negative?
Has the cancer spread to my lungs or elsewhere?
Does the fracture change my treatment or surgery?
Is limb-sparing surgery possible for me?
How often will I need follow-up imaging, and for how long?