What is Cancer (Malignancy)?
A cancer or malignancy has two defining features that make it very different from normal tissue. These are:
- Uncontrolled growth
- The capacity to spread to other organs
Uncontrolled growth does not stop even though it damages surrounding tissue. In the lung a tumour will continue to grow despite blocking airways and causing infection or difficulty in breathing. In the brain a tumour will continue to grow, pressing on surrounding tissue, leading to personality change or fits. The primary tumour is the group of cells in an organ that grew first, these will usually cause symptoms depending on where they are.
The capacity to spread gives rise to secondary growths at a distance from the primary tumour. These are called ‘secondaries’ or ‘metastases’. Sometimes the primary may be unknown (diagnostic label ‘unknown primary’) but a person develops symptoms from ‘secondaries’.
What are secondary tumours (metastases)?
In addition to uncontrolled growth, the primary tumour may leak cells into the blood or lymphatic system, which travel around the body. Some of these cells may take up residence in tissues far away from the primary tumour and cause symptoms there. These cells reproduce themselves making colonies; the larger the colony the more likely they are to cause symptoms. The lung, brain, liver and bones are common areas for this to happen, lung ‘secondaries’ may cause shortness of breath or pneumonia and brain ‘secondaries’ may cause fits or personality change. The effect of the ‘secondaries’ depends on where the abnormal cells start growing and what that part of the body does.
Cancer cells tend to retain some features of the cells from which they arose and cancer cells from different areas therefore behave differently. By behaviour we mean rate of growth, response to treatment or a preference to metastasise to particular organs in the body. They require different types of treatment and some cancers are much more curable than others. Cancers that grow rapidly and spread quickly may be called ‘aggressive’, ‘anaplastic’ or ‘high-grade’. Cancers that grow slowly and spread less quickly or hardly at all are referred to as ‘low-grade’ or ‘indolent’. The likely behaviour of a cancer can be predicted from the appearance of the cells under the microscope. A ‘biopsy’ of a tumour means taking a small sample of cells from the tumour to look at under the microscope. Information about the cells from microscopic examination is used to confirm the presence of cancer, to plan treatment and to provide information to patients about treatment needed and likely outcome.
What are ‘benign’ tumours and are they dangerous?
‘Benign’ means that a tumour or growth will not metastasise or spread around the body in the way that a ‘malignant’ or cancerous growth does. However these can still be dangerous to health and have disabling effects. The most common example of this is the ‘benign’ brain tumours. These tumours do not spread and are slow growing. In the majority of cases they can be removed by surgery and cured. However sometimes these tumours are located in areas of the brain, which carry out important functions such as enabling us to breathe and remain conscious. Removing them presents too high a risk of causing death or leaving a person in a coma. These tumours are very hard to manage as they do not respond well to other forms of treatment in the way that fast growing malignant tumours do. Other tumours may also have dangerous effects even though they are benign and include tumours which produce hormones such as phaeochromocytoma (a tumour of the adrenal gland which produces large amounts of adrenaline) or tumours, which prevent hormones being released such as tumours of the pituitary gland, which when they are very large can also press on the optic nerves (nerve to the eye) and cause blindness e.g. homonymous hemianopia – refer to Vision guidance
