Risks and causes of soft tissue sarcomas

Soft tissue sarcomas are rare cancers. Around 2,300 people are diagnosed with soft tissue sarcomas each year in England. The classification of soft tissue sarcomas has recently been agreed in the UK. Statistics for Wales and Scotland will soon be available.

We don’t know exactly what causes soft tissue sarcoma. But there are a number of risk factors associated with this condition. A risk factor is anything that may increase your risk of developing a particular type of cancer. If you have a risk factor it does not mean that you will definitely develop cancer. You can develop a cancer even if you have no known risk factors.

Soft tissue sarcoma can be diagnosed at any age, but as people get older they are more likely to develop it. Around two thirds are diagnosed in people over 50 years old. Soft tissue sarcomas account for 1 in every 14 cancers diagnosed in children. Just over half of these are a specific type called rhabdomyosarcoma.

Radiotherapy treatment for other cancers can sometimes cause a sarcoma in the treatment area years later. This is because the radiation can affect healthy tissue in the treated area. A radiation induced sarcoma does not usually develop for at least 5 to 10 years after the original treatment. In some people it may occur 20 to 30 years later. Only 3 out of every 100 soft tissue sarcomas are due to previous radiotherapy.

Radiotherapy and surgery for breast cancer can cause lymphoedema of the arm. About 1 in every 3,000 women who have breast removal (mastectomy) and get chronic lymphoedema develop a type of sarcoma called lymphangiosarcoma. This is also known as Stewart-Treves syndrome. We must stress that this can take many years to develop and is very rare.

Thousands and thousands of people have radiotherapy every year, so this really is a small risk. If you are having radiotherapy for cancer, it is important to keep in mind how much good the treatment is doing you. The cancer you are being treated for is much more of a danger to you than the small risk of getting a sarcoma in the future. Radiotherapy treatment is now planned very precisely and very little healthy tissue is included in the radiation field. We hope that these improvements in radiotherapy planning may further reduce the number of sarcomas that radiotherapy causes.

Some types of rare genetic conditions can increase your risk of getting a sarcoma. These are

• Neurofibromatosis
• Li Fraumeni syndrome
• Retinoblastoma

If any of these conditions run in your family you are likely to know.  A genetic condition can crop up in a family that has not had it before but this is very rare.

Neurofibromatosis is a genetic disease in which non cancerous (benign) tumours form in the nerves under the skin and in other parts of the body. This increases the risk of getting a very rare type of sarcoma called a malignant peripheral nerve sheath tumour (MPNST). About 8 to 14% of people with neurofibromatosis will have a MPNST at some point in their life. Neurofibromatosis is also called von Recklinghausen disease.

Li Fraumeni syndrome is a genetic syndrome that causes several different types of cancer to occur in affected families. It is sometimes called family cancer syndrome. Families with Li Fraumeni syndrome have a higher risk of breast cancer, brain tumours, leukaemias and other cancers. They also have a higher risk of developing soft tissue sarcoma. About 17 to 18% of tumours in people with Li Fraumeni syndrome are soft tissue sarcomas.

Retinoblastoma is a type of inherited eye cancer. It is nearly always diagnosed in childhood. Children who have had retinoblastoma have an increased risk of developing a soft tissue sarcoma in the future. About 13% of children who have retinoblastoma develop a soft tissue sarcoma within 50 years. The radiotherapy given as treatment for retinoblastoma may partly account for the increased risk. These children also also have an increased risk of getting a type of bone cancer called osteosarcoma.

We don't have clear evidence for whether exposure to particular chemicals can cause soft tissue sarcoma. It is often hard to tell how much people have been exposed to particular chemicals. The number of cases of sarcoma in the studies is also usually very small. Several chemicals are thought to increase the risk of some types of sarcoma and these include

• Vinyl chloride
• Dioxins
• Chlorophenols

Vinyl chloride

Vinyl chloride is a chemical used in making some plastics. It is thought that it may increase the risk of sarcoma of the liver. But it is not clear whether this chemical can cause sarcomas elsewhere in the body. 

Dioxins and chlorophenols

Dioxins are produced in industries related to paper bleaching and pesticide making. They are also present in low levels in the air and in some foods. Chlorophenols are found in pesticides and antiseptics and present at very low levels in drinking water disinfected with chlorine. These chemicals were linked to an increased risk of sarcoma in Swedish studies in the 1990. But several more recent studies found no increased risk through exposure to these chemicals at work or in the general environment.

Kaposi’s sarcoma is an unusual type of soft tissue sarcoma that develops from cells in the blood vessels. Kaposi's sarcoma is caused by Human Herpes Virus-8 infection (HHV-8), which is also known as Kaposi's sarcoma associated herpes virus (KSHV). Many people have HHV-8 and most do not develop Kaposis sarcoma. But this virus is sometimes able to cause Kaposi's sarcoma in people with lowered immunity.

HIV and AIDS cause lowered immunity and about 8 out of 10 people who get Kaposi's sarcoma have HIV or AIDS. People taking medicines to suppress their immunity (usually after an organ transplant) also have an increased risk of developing Kaposi’s sarcoma. One study also found an increased risk of skin sarcomas (cutaneous sarcomas).

An infection called Epstein Barr virus (EBV) has been linked with leiomyosarcomas in children and young people with HIV or AIDS. It has also been linked to leiomyosarcoma in adults taking medicines to lower immunity after a transplant. But only a small number of cases have been recorded in medical journals. There are also a small number of reports of people developing angiosarcoma after kidney transplant.

It is not clear whether smoking affects the risk of developing soft tissue sarcoma. One large American study showed that smokers have a higher risk of dying from soft tissue sarcoma than non smokers. But an Italian study showed no increase in risk. Some studies have shown that smoking reduces Kaposi's sarcoma risk but other studies showed no difference. So we need more research to clarify this.

One study has shown an increased risk of Kaposi's sarcoma in people who have diabetes. But another study showed no increased risk. So the situation is unclear at the moment.

Sometimes people think that an injury has caused a cancer. There is no evidence that an injury of any kind can cause a sarcoma. But an injury may draw attention to a sarcoma that was already there if the person has X-rays or scans. Cancers take many years to develop. In most cases where people think an injury is responsible, the injury has only happened recently and so is unlikely to be linked to the cancer.