Chemotherapy is not usually a single treatment, but a course of treatments. A course usually takes between 3 to 6 months, but can be more or less than that. During that time, you would probably have between 4 to 8 cycles of treatment.
A cycle includes the time when you have your chemotherapy treatment and then a break before the next treatment, to allow your body to recover. So if your cycle lasts 4 weeks, you may have treatment on the 1st, 2nd and 3rd days and then nothing on the 4th to the 28th day. Then the cycle starts again. Or, as another example, you may have a 3 week cycle, where you have treatment on the 1st and 8th days, but nothing on days 2 - 7 and days 9 - 21. The treatment may include one or more intravenous chemotherapy drugs and may include chemotherapy tablets or capsules.
Depending on the drug or combination of drugs, each treatment lasts from a few hours to a few days. You may have treatments every week or every 2, 3 or 4 weeks, depending on the drugs and your treatment plan. Your doctor may refer to this as your chemotherapy regime (or chemotherapy regimen). If you're having chemotherapy as tablets you may take smaller doses daily for a few days or for many weeks or months. Then you'll have a rest period.
Why cycles of treatment?
There are a couple of good reasons why you have chemotherapy as a course of treatments over a few months. Firstly, it allows the chemotherapy to kill more cancer cells. At any one time, some of the cancer cells will be resting. Chemotherapy only attacks cells that are in the process of dividing (splitting into two). So resting cells will not be killed. Some of the cancer cells that were resting during your 1st treatment will be dividing by the time your 2nd comes around and so will be killed off. There is more about this in this section about how chemotherapy works.
The second good reason for giving treatment in cycles is that the rest between treatments allows your body to recover from any side effects. Normal cells usually repair the damage from chemotherapy more effectively than cancer cells, so damage to cancer cells should progressively build up without causing permanent damage to normal cells.
How your doctor chooses your treatment
The exact regime that your doctor chooses depends on a number of factors
The type of cancer you have
Where it is in your body
Whether it has spread
Where it has spread to (if it has)
Your doctor will also take your general health and fitness and your age into account. Some drugs have more of an effect on your body than others. Your doctor has to judge that you are well enough to be able to cope with any side effects of the treatment before you start. How often you have each cycle, and how long your treatment course lasts, also depends on many factors including
The type of cancer
The drugs used
How the cancer cells respond to the drugs
Any side effects from the drugs
Number of treatment cycles
All the treatment you are offered is based on years of research. The research will have compared different ways of giving the chemotherapy and different numbers of treatments. The people given chemotherapy in those clinical trials will have been followed up to see how they did. The combination of drugs your doctor suggests will be the best of all those tested. Usually, it takes several months to complete your course of chemotherapy treatments. You need to have enough courses to kill the cancer. But not so many that you develop severe or permanent side effects.
When you have chemotherapy through an infusion pump you can have the drugs
All the time for a few months (continuous administration)
For a few days each month
For a few weeks
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