A syndrome is a group of symptoms which characterise a particular illness.

There are three things which commonly make up Pancoast syndrome (rather confusingly, one of these is another syndrome). These are:

• pain in one shoulder which goes down that arm,
• damage to the first rib on that side
• Horner's syndrome (narrowing of the pupil of the eye, drooping of the eyelid, loss of sweating of the skin of the face)

Pancoast syndrome is almost always caused by a lung cancer that has developed at the top (or apex) of the lung, which is very close to the first rib. Lung cancers which occur in this position are often called Pancoast tumours. ( They are also called apical lung cancers or superior sulcus tumours). Pancoast syndrome can be caused by non-cancerous conditions but this is rare.

Pancoast tumours are uncommon and tend to be quite slow growing and often give rise to pain in the shoulder region for many months before they are finally diagnosed. They also tend to be less likely to spread to other parts of the body than lung cancers starting in other areas of the lungs. One reason that they are difficult to diagnose is that, because of their position at the top of the lung, they do not show on chest x-rays until they have reached an advanced stage.

When tissue from Pancoast tumours is examined under the microscope they are usually non-small cell lung cancers. This is the commonest type of lung cancer, making up about 80% of lung tumours, although only a minority of these are Pancoast tumours.

Whenever possible the treatment of a Pancoast tumour is an operation to remove the growth (usually with some radiotherapy treatment given either before, or after surgery). Chemotherapy may be used at the same time as the radiotherapy (called chemo-radiotherapy) to try and improve the shrinkage of the cancer. If the cancer is too advanced for an operation then radiotherapy can be given to try and control it and ease symptoms such as pain.