Intimal Sarcoma, from the CureRays guide library.

Intimal sarcoma is a rare, aggressive cancer that grows inside the wall of large blood vessels or the heart — most often the pulmonary artery — and is frequently mistaken at first for a blood clot.

What it is.

Intimal sarcoma is a very rare cancer that arises from the innermost lining (the intima) of large blood vessels and the heart. By far the most common site is the pulmonary artery, the great vessel that carries blood from the heart to the lungs; it can also appear in the aorta or the heart chambers. Because the tumor grows inside the vessel and blocks blood flow, its symptoms — shortness of breath, chest pain, fainting — look exactly like a pulmonary embolism (a blood clot), so it is often misdiagnosed and treated as a clot before the truth is found. Most intimal sarcomas carry extra copies of a gene called MDM2, which pathologists test for to confirm the diagnosis. It is an aggressive cancer that grows quickly and tends to spread to the lungs, but complete surgical removal, sometimes helped by radiation and chemotherapy, offers the best chance of extending life.

How radiation treats it.

Radiation damages the DNA inside cancer cells so they can no longer divide. For intimal sarcoma — which sits against the heart and great vessels — modern radiation is delivered with image guidance that accounts for both breathing and the beating heart, so the dose stays locked on the tumor while sparing healthy heart muscle and lung. Used before surgery, it can shrink the tumor and tighten its margins to make removal more complete; used after surgery, it lowers the chance the cancer returns where it started. It is painless, given as short daily sessions, and leaves no radioactivity behind.

The ways we can treat it.

Neoadjuvant (pre-surgery) radiation. Image-guided radiation given before the operation can shrink the tumor and firm up its edges, increasing the chance the surgeon can remove it completely and reconstruct the vessel.

Conformal / IGRT photon radiation. Intensity-modulated, image-guided beams shape the dose around a tumor sitting against the heart, lungs, and great vessels while accounting for the motion of breathing and the heartbeat.

Stereotactic body radiation (SBRT). Delivers a few high, focused doses to an isolated metastasis (for example in the lung) when surgery is not the right option.

Questions we hear often.

Why was I first told I had a blood clot? Intimal sarcoma grows inside a large vessel and blocks blood flow, producing the same symptoms and scan appearance as a pulmonary embolism. Many patients are treated for a clot first; the cancer is suspected when the 'clot' doesn't respond to blood thinners and grows. Specialized imaging and a biopsy confirm the diagnosis.

Can it be cured? It is an aggressive cancer, but complete surgical removal — often with reconstruction of the affected vessel — offers the best chance of long-term control and is associated with the longest survival. Radiation and chemotherapy are added to improve the odds, especially when removal is difficult.

How does radiation fit in if the tumor is next to my heart? Modern radiation accounts for the motion of breathing and the heartbeat, so the beam stays focused on the tumor while protecting healthy heart and lung. It can be used before surgery to make removal more complete, after surgery to prevent local return, or to treat an isolated area of spread.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.