Benefits, risks and side effects of treatment

Doctors and other health professionals often use statistics when talking about cancer treatments. Knowing some statistics can help you to make decisions about your treatment.

Statistics are a way of giving you information using numbers. Treatment statistics are based on the experiences of large numbers of people.

You may be given statistics as percentages, bar charts or pie charts. Doctors may use statistics to explain how well a treatment might work or the how likely certain side effects are. If your doctor uses statistics that are difficult to understand, ask them to simplify them. It may also help if they write them down for you to look at later with a family member or friend.

Doctors also often talk about the benefit or risk of a treatment.

  • A benefit is the chance that something good or helpful may happen as a result of doing (or not doing) something.
  • Risk is the chance that something harmful or unwanted may happen as a result of doing (or not doing) something.

Using statistics, benefit and risk to decide on treatment

Healthcare professionals may use statistics to tell you what they know about a particular treatment. They sometimes explain things using the terms benefit and risk.

Your doctor may use statistics to tell you what they know about a particular treatment. They are a way of presenting information (also called data) using numbers. We come across statistics in many areas of daily life – not just in healthcare. They can be useful when making decisions about treatment.

For example, information about a new drug may include data on:

  • how effective it is for someone in your situation
  • possible side effects
  • how severe the side effects are
  • how many people are affected by the side effects.

It’s important to remember that statistics are based on large numbers of people. They can’t tell you what is going to happen to one individual, but they can give you an idea of how likely it is.

For example, if you’re offered a drug that causes nausea (feeling sick) in 80% of people (80 out of 100), you don’t know exactly whether you will feel sick or not, but it is quite likely. But if you’re offered a different drug that causes nausea in just 30% of people (30 out of 100), it’s a lot less likely that you will feel sick.


Understanding statistics

Statistics can be complex and difficult to understand. You may feel that they make it more difficult for you to make your decision but the following section aims to explain the different ways that statistics can be helpful. You may want to skip this section if you don’t think statistics will be useful, or you could ask someone else to read it for you.

If your doctor uses statistics that make things more confusing, ask them to simplify things for you. It may help if they write the statistics down. Then you can look at them later or ask a relative or friend to go through them with you.

There are different ways of showing statistics. These include:

  • percentages
  • bar and pie charts
  • other diagrams.

The following example shows how information can be presented in different ways. This is just an example and does not refer to any real medicine or research. It shows that you should consider both how effective the treatment is and its possible side effects when making your decision.

A doctor recommends a new drug to someone who is about to start chemotherapy, as it can help prevent hair loss. Before agreeing to have this new drug, the person may want to know about the side effects, how many people had side effects and whether some people had no side effects.

The doctor tells them that in a study of 100 people, the side effects included:

  • headaches
  • feeling tired
  • a sore throat.

In the study:

  • 50 people had headaches = 50%
  • 80 people felt tired = 80%
  • 25 people had a sore throat = 25%.

And some rarer side effects were found too:

  • 1 person had an allergic reaction = 1%
  • 2 people had very itchy skin = 2%
  • 4 people had a stomach ache = 4%.

Some people had no side effects at all, while others had a few different side effects.

The same information can be shown using a diagram. For example, this bar chart shows types of side effects of chemotherapy:

Understanding statistics
Understanding statistics

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The person making the decision may also want to know if the drug helped to prevent hair loss.

The doctor explains the results of the study.;

Of the 100 people who took the new drug:

  • 10 had no hair loss
  • 23 had minimal hair loss
  • 37 had a lot of hair loss and had to get a wig
  • 30 people had total hair loss and had to get a wig.

Overall, the new drug slowed down or stopped hair loss for 70 people, but 67 of the 100 people still needed to get a wig despite having the drug. 

The numbers are a lot to think about and the information may be clearer to see in diagrams.

The pie chart shows how many people had hair loss after chemotherapy and whether they needed a wig:

An example of statistics about hair loss
An example of statistics about hair loss

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Benefit and risk

Healthcare professionals sometimes explain things using terms such as benefit and risk. A benefit is something good or helpful that happens as a result of doing (or not doing) something. For example, a benefit of eating a healthy diet is that you’re less likely to be overweight and therefore less likely to develop diseases such as heart disease, diabetes and some cancers.


Benefit

A benefit is something good or helpful that happens as a result of doing (or not doing) something. For example, a benefit of eating a healthy diet is that you’re less likely to be overweight and therefore less likely to develop diseases such as heart disease, diabetes and some cancers.

A benefit of cancer treatment may be that the cancer is cured or controlled for some time. A benefit can also be that the situation doesn’t get worse. For example, the cancer may stay the same size or grow at a slower rate.


Risk

Risk is the chance that something harmful or unwanted may happen as a result of something. This could be a procedure, test or treatment. Or it may be the result of not doing anything.

Life experiences may affect our view of risk, the decisions we make and the action we take. Our views of risk are likely to change at different times in our lives depending on our circumstances.

For example, if you know someone who has had lots of side effects from having chemotherapy, your view about the risks of chemotherapy is likely to be different from someone who doesn’t know anyone who’s had it. These experiences can influence your behaviour and may make you less likely to have chemotherapy.

In this example, it’s important to remember that there are lots of different chemotherapy drugs and that not all of them cause lots of side effects. There are also some very good drugs to help prevent or reduce side effects.

Describing risk

Risk can be described in different ways. Healthcare professionals often describe situations as low risk or high risk. These words can mean different things to different people. Using numbers can sometimes be clearer.

Numbers can be shown in different ways. A doctor may describe risk using percentages (%), fractions or likelihood.

For example, 25 out of 100 can be described as:

  • 25%
  • ¼
  • 0.25
  • 25 in 100.

Types of risk

When describing risk, research papers and doctors sometimes talk about absolute risk and relative risk.

Absolute risk is the likelihood of something happening to a person. For example, the risk of developing a certain illness in your lifetime may be 1 in 10. This can also be described as a 10% risk.

Relative risk compares risk in two different groups of people. An example would be the risk of developing lung cancer in smokers and non-smokers.

The following example may help explain absolute risk and relative risk. This is just an example and does not refer to any real medicine or research.

The doctor tells you that:

  • You have a 6 in 100 (or 6%) risk of developing disease A at some point in your life.
  • Research shows that if you take drug X, your risk changes from 6 in 100 to 3 in 100 (or 3%).

The reduction in risk can be described in two ways:

The absolute risk of developing the disease without drug X is 6%, but with drug X it is 3%. So the absolute risk reduction is 3%.

In this example, the risk has been reduced by half (from 6 to 3). A half can also be described as 50%, so the risk has been reduced by 50%. This is the relative risk reduction.

Relative risk reduction often sounds more dramatic than the absolute risk reduction and is used more often to describe how effective a treatment is.

We can see from this example how the way that risk is shown may influence decision making. Risk and how it relates to you can sometimes be difficult to understand. Ask your healthcare team to explain things in more detail if you’re not sure.


Back to Coming to your decision

Finding out your treatment options

Knowing basic information about your type of cancer and different treatments options can help you to make an informed treatment decision.

Making your decision

If  you’re struggling to come to a decision about treatment, try following these five steps.