What is intimal sarcoma?

Where it grows, and what the name means

Intimal sarcoma is a cancer that starts in the wall of a large blood vessel — in the layer called the intima, the smooth inner lining. It is a sarcoma, the family of cancers that arise from connective tissue rather than from glands or skin. In the current WHO classification of tumours it is a distinct entity of its own, not a variant of angiosarcoma or leiomyosarcoma.¹

It grows in a small number of places:²³

• The pulmonary artery — the vessel that carries blood from the heart to the lungs. This is the most common site; the pulmonary trunk and the right main pulmonary artery are affected most often.⁴ Pulmonary vessel intimal sarcomas are roughly twice as common as aortic ones.³
• The heart itself — usually the left atrium. These are often called cardiac intimal sarcomas or, in older reports, "undifferentiated cardiac sarcomas".⁵
• The aorta — the body's main artery, mostly the abdominal part (about 70%), less often the thoracic part.³
• Rarely, other large arteries (coronary, iliac, femoral) or the pulmonary veins.

Because the tumour grows inside the vessel, it behaves differently from most cancers: it blocks blood flow, and pieces of it can break off and travel downstream — which is exactly what a blood clot does. That single fact explains most of what makes this disease so hard to recognise.

How rare is it?

Very. The entire medical literature contains only a few hundred described cases of pulmonary artery intimal sarcoma, and fewer of the aortic and cardiac forms.⁹ The largest pooled analysis to date gathered 643 pulmonary artery sarcoma patients from ten years of published reports worldwide.⁴ Most oncologists, cardiologists and lung specialists will never see one in their whole career.

Typical age at diagnosis is the late 40s to early 60s — a mean of 48 years for pulmonary artery tumours, about 50 for cardiac and about 62 for aortic ones — with men and women affected roughly equally.³⁴

That rarity is the reason this website exists. With numbers this small, no single hospital ever collects enough cases to learn from, and there is no registry that pools them. Every documented case really does change what is known.

Symptoms, and why it is so often mistaken for a blood clot

There is no symptom specific to intimal sarcoma. For pulmonary artery tumours the usual complaints are shortness of breath (by far the most common), chest or back pain, a persistent cough, sometimes coughing up blood, light-headedness or fainting, and weight loss or fever.² Aortic tumours may cause pain in the belly, back or legs, or symptoms from blocked blood flow to a limb or organ.²

These are the same symptoms as a pulmonary embolism (a blood clot in the lung), which is a thousand times more common. On a CT scan the tumour also looks like a clot filling the artery. In the pooled analysis of 643 patients, 70.6% were first diagnosed with pulmonary embolism, and only 15.4% were suspected of having a sarcoma from the start.⁴ In one hospital series, 21 of 22 patients (95.5%) were initially misdiagnosed.⁶

Clues that point away from a clot and towards a tumour include: no response to blood-thinning treatment, a single large filling defect that expands the artery, uneven density on CT, tissue that takes up contrast, and — very characteristically — strong uptake on an FDG-PET/CT scan, which a blood clot does not show.⁷⁴ If you or a relative were treated for a "clot" that never went away, this is the pattern that eventually leads to the right diagnosis.

How it is diagnosed

Diagnosis usually follows three steps:²⁹

1. Imaging — CT pulmonary angiography, cardiac or vascular MRI, and increasingly FDG-PET/CT, which showed suggestive findings in 93.9% of pooled cases.⁴
2. Tissue — a biopsy (through the airways, through the skin, or via a catheter inside the vessel) or, very often, the tissue removed at surgery. Sometimes surgery is done for a suspected clot and the diagnosis is only made afterwards by the pathologist.
3. Pathology with molecular testing — under the microscope, intimal sarcoma looks like many other high-grade sarcomas. What confirms it is the combination of the location and a characteristic gene change: amplification of the gene MDM2 (extra copies of it), found in roughly two thirds or more of cases, often together with CDK4 and PDGFRA.⁵⁸ Pathologists test for this with immunohistochemistry (MDM2 and CDK4 staining), FISH, or sequencing. Our page on reading your pathology report explains these terms line by line.

Because the tumour is so easily confused with other things, a review of the slides by a sarcoma pathologist at a reference center is standard good practice — see getting a second opinion.

What causes it?

Nobody knows what triggers it. What is known is what the tumour cells look like genetically: instead of the many small mutations seen in smoking- or sun-related cancers, intimal sarcoma is driven by gene amplification — the cell has made many extra copies of a short stretch of chromosome 12 that contains MDM2 and CDK4, and often of a stretch of chromosome 4 that contains PDGFRA.⁵⁸ Researchers think this is what pushes the cell to keep dividing.²

There is no known lifestyle cause and no evidence that it runs in families. It is not infectious, not caused by anything you did, and there is nothing you could have done to prevent it.

How the disease behaves

Intimal sarcoma tends to grow along the inside of the vessel and into its wall, obstructing blood flow. It can shed tumour fragments downstream (into the lungs from the pulmonary artery, into organs or limbs from the aorta), and it can spread through the bloodstream to the lungs, bones, liver and elsewhere.³⁹ After surgery it can come back locally — at the site where it was removed — or as distant metastases.

The disease is aggressive, and the published survival figures are sobering. They are also, in our view, incomplete and probably too pessimistic for some patients — we go through the actual numbers and how to read them on the prognosis and survival page.

If you have just been diagnosed: three things that matter most

1. Get to a sarcoma reference center. Not because your local hospital is bad, but because this diagnosis needs people who have seen it before: sarcoma pathologists to confirm it, cardiothoracic or vascular surgeons used to operating inside the pulmonary artery or aorta, and oncologists who know the small evidence base. Management in a specialised multidisciplinary center is the one recommendation every review agrees on.⁸ How to find one →
2. Ask whether complete surgical removal is possible. Surgery is the only treatment that can potentially cure this disease, and complete removal is the single strongest factor in every outcome series.⁴⁸ Treatment options →
3. Get the molecular profile — and a copy of it. Ask that the tumour is tested for MDM2/CDK4/PDGFRA and, ideally, sequenced with a broad panel. It confirms the diagnosis, it is what any targeted treatment or trial will be based on, and it is what you can compare with other cases. What the report means →

And one more: you are allowed to ask questions. We wrote down the ones we wish we had asked.

Frequently asked