produce chemical factors that enable them to grow as a group, and we are only just beginning to understand the growth factors involved in sustaining cancer cell growth. In future, we may be able to devise anti-cancer drugs that can block these growth factors.
Classifying cancer
Cancer can strike any organ of the body, each with its own pattern of behaviour. There are currently 208 classifiable sites at which cancers arise, and many of these are broken down into further subtypes. This reflects the many different cell types that make up the human body, many of which can grow out of control.
Tumours are named according to the site at which they originate, not by the organs they spread to. For example, a patient with breast cancer that has spread through the bloodstream to the liver is said to have metastatic breast cancer. If it then spreads to the bone, it is still breast cancer, but metastasized to bone. On the other hand, it is possible to have a primary bone or liver cancer, which has arisen in these tissues and metastasized elsewhere. This may cause confusion because of poor communication in rushed clinics.
Tumours are also named to reflect the type of structure from which they have come. A carcinoma, for example, comes from cells lining body cavities called ‘epithelial cells’. Such cells are found in the lungs, colon, breast and prostate gland. Carcinomas are by far the most common type of cancer. Tumours derived from the body’s structural tissues, muscles, tendons, bones and cartilage are called ‘sarcomas’. Those arising from the lymphatic system are called ‘lymphomas’, and cancers of the white blood cells and bone marrow are known as ‘leukaemias’.
If you ever hear any terms used to refer to your particular cancer which you do not understand, ask for an explanation. Cancer classification is complicated, and there are often several words that mean much the same thing. If you don’t understand a term, don’t go away feeling too embarrassed to ask what it means – check it out and save yourself unnecessary stress.
How is a cancer diagnosis usually made?
The only way to diagnose cancer definitively is to test a sample of abnormal cells from the site of the tumour. The usual way of doing this is to obtain a biopsy, or a small tissue sample, under either a local or general anaesthetic, depending on the site of the tumour.
Cancer has no specific symptoms – it depends on where the tumour is, how big it is, which structure it is invading and whether it has spread to other parts of the body. A patient with lung cancer, for example, may have a cough with or without blood or phlegm, or a persistent chest infection that does not respond to antibiotics. The usual symptom of breast cancer is a lump in the breast, although it may well have spread by the time it can be detected this way. If it has spread, then its symptoms will depend on the site of the metastases – in the lungs, it may mimic a lung tumour; in the liver, a liver tumour, and so on.
Because cancer produces so many different types of symptoms which can be mistaken for minor illnesses, there may be a period of several weeks with repeated visits to the GP before the symptoms are taken seriously. The best rule of thumb is that any progressing symptom that does not disappear after two to four weeks should be further investigated. Usually, this involves being referred to a hospital where the investigations can be done rapidly.
If cancer is suspected, there are two important requirements: to do a biopsy to find out exactly what type of cells have gone wrong and, therefore, how best to treat them; and to ‘stage’ the disease to find out how far the disease has spread as this, too, dramatically affects not only the optimal treatment, but also the likely outcome.
The tests to determine the site and stage of the cancer include:
• Biopsy, to study a piece of tissue thought to be cancerous – the definitive way to make the diagnosis
• Blood tests, to check for anaemia, bone-marrow function, liver and kidney function, and search for tumour markers – substances produced by cancer cells and detectable in the blood, thereby alerting doctors to the presence or spread of cancer
• Plain X-rays, to provide information about various parts of the body
• Contrast X-rays, injecting or ingesting a radiopaque substance to increase what can be seen on the X-ray
• CT (computed tomography) scans, to provide detailed information about the structure of various internal organs
• MRI (magnetic resonance imaging), a powerful imaging technique based on magnetic field shifts in the body
• Bone and liver scans, to show areas of dysfunction in the bone and the liver that may be due to the spread of a cancer.
Staging
Determining how far a cancer has spread is a critical starting point before deciding on treatment. There are several systems available and this often causes confusion, even among doctors.
One of the most commonly used staging systems is the TNM system, developed by a committee of the International Union Against Cancer. Here, the letter T stands for ‘tumour’, with T1 referring to a small tumour and T4 referring to a very large one.
The N stands for ‘nodes’, the lymph nodes draining the organ in which the tumour is found. Enlarged nodes containing growing tumours are classified as N1 or N2 depending on their site and number.
The M stands for ‘metastasis’ (spread) and is either present (M1) or absent (M0).
Other staging systems are often simpler. Early-stage disease may be called stage 1 whereas late-stage disease, or more advanced cancer, is then stage 4. Different criteria may be used for cancer at different sites of the body, so ask your consultant to explain exactly what the staging means for your type of cancer. A person with disease that has not spread is likely to have a better outcome than a patient whose disease has already left its primary site. This is because a localized tumour is more likely to be cured or removed altogether by either surgery or radiotherapy.
Grading
The grade of a cancer, determined by the pathologist by looking at the cancer cells through a microscope, is also useful in predicting the outcome of a cancer. A high-grade tumour contains very abnormal cells, which have mutated greatly, grown rapidly and often spread throughout the body. This is also referred to as ‘poorly differentiated’. At the other end of the spectrum are low-grade tumours, which can look similar to the tissue from which they have been derived and are referred to as ‘well differentiated’. Such tumours grow more slowly and are less likely to spread quickly. The outlook is usually better for low-grade tumours, but there is a paradox. High-grade aggressive tumours are often more sensitive to chemotherapy as the chemicals work best against the most rapidly dividing cells in the body. Unfortunately though, rapidly growing cells can continue to evolve and can become resistant to specific drugs rather rapidly, too.
It is also possible to have varying opinions as to the grade of a tumour among pathologists. So, if you are in any doubt, or the pathology seems uncertain, ask for a second opinion from another pathologist.
Secondary cancer
Cancer that develops in the body away from the site of the original tumour is called a ‘secondary cancer’ or a metastasis. These may be found at the time of diagnosis or they may develop later on. If secondaries appear, it can often be a more severe blow than the original diagnosis.
Cancer can spread around the body by:
• invading local tissues
• entering the lymphatic system and lymph nodes
• entering the bloodstream and travelling to distant sites