A desmoid tumour is a rare type of tumour that develops in the fibrous tissue that covers muscles and other organs. It is also sometimes called desmoid-type fibromatosis or aggressive fibromatosis.

Most doctors agree that desmoid tumours aren't cancers because they can’t spread to other parts of the body, although they can grow into surrounding tissues. They are usually slow-growing and the first sign is often a painless or slightly painful lump.

Many desmoid tumours occur in the tummy area (abdomen) or in the pelvis. Other parts of the body that can be affected include the chest, shoulders, thighs and the head and neck area. They can affect people of any age and sometimes are found in children.

The cause of most desmoid tumours is unknown but inherited genes are sometimes involved as they can run in families. Hormones can be a factor in some desmoid tumours. While, for some people, physical factors such as an earlier injury may be a trigger.

Although desmoid tumours are rare sometimes more than one person in a family is affected. In particular, people with an inherited condition called family adenomatous polyposis (FAP), have a much higher risk than average of developing them. FAP is mainly linked to an increased risk of bowel cancer. But, about 1 in 10 people with FAP develop desmoid tumours.

In children desmoid tumors affect boys and girls equally. However, in adults they are more common in women. Pregnant women or women who have had a baby within the past two years are affected more than average. So, it is thought that female hormones such as oestrogen may sometimes have a role in triggering the growth of a tumour.

Trauma to a particular area of the body may, occasionally, trigger the growth of a desmoid tumour there. The trauma could be an injury, an operation or radiotherapy. Desmoid tumours, that occur in people with FAP, often develop in an area that has previously been operated on.

The most common first sign of a desmoid tumour is a painless lump growing deep under the skin. But, symptoms vary depending on where the lump is and its size. If the mass is pressing on nearby nerves, organs or muscles this might cause pain. Rarely a tumour growing in the tummy or pelvis may cause of blockage of the bowel or bleeding from the bowel.

A number of tests may be done to diagnose the tumour and help the doctors to plan the best treatment. These may include X-rays, ultrasound, CT or MRI scans and taking a sample from the tumour (a biopsy) to be looked at under the microscope.

Treatment depends on; where the tumour is, its size, how quickly growing it is and whether it is causing symptoms. If you have the condition FAP this may also affect what treatments are best for you.

Treatment may include one or more of:

• surgery
• radiotherapy
• chemotherapy
• hormonal therapy
• anti-inflammatory tablets

The most commonly used treatment is surgery to remove all of the tumour. Unfortunately, tumours sometimes grow back. Other treatments may be given after surgery to try to reduce the chances of this happening.

When an operation isn't possible, radiotherapy may be used to shrink the growth or to stop it increasing in size. Because the tumours are often slow growing, it may take months before the effects of radiotherapy can be seen. So, it may be several months before a scan can show whether the tumour has shrunk or stopped growing as a result of the treatment.

Occasionally, a desmoid tumour completely disappears without any treatment. This is called spontaneous regression. Or, sometimes a desmoid tumour grows quickly then stops growing. Because of this, in some situations, doctors may keep the tumour under observation rather than treat it at once.