Statistics, benefits and risks of cancer 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.

Statistics

Your doctor may use statistics to tell you what they know about a treatment. Statistics are a way of presenting information 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 drug may include statistics on:

  • how effective it is
  • possible side effects
  • how severe the side effects are
  • how many people are affected by the side effects.

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

For example, some drugs can cause nausea (feeling sick) in some people. If a drug you are offered causes nausea in 80 out of 100 people (80%), you cannot know exactly whether you will feel sick or not, but it is quite likely. If you are offered a different drug that causes nausea in just 30 out of 100 people (30%), it is a lot less likely that you will feel sick.


Understanding statistics

Statistics can be complicated and difficult to understand.

You may feel that they make it more difficult for you to make your decision, but the following information aims to explain the different ways that statistics can be helpful.

If your doctor uses statistics that confuse you, ask them to make the information simpler. 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.

Ways of presenting information

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 talks to someone who is going to start chemotherapy about a new drug which may help prevent hair loss.

Before taking the drug, the person wants to know how well the drug works to stop hair loss.

The doctor explains the results of a study. Of the 100 people who took the new drug:

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

In total, the new drug slowed down or stopped complete hair loss for 70 people (10+23+37), but 67 of the 100 people who took the drug had to get a wig.

The numbers in each group can be shown in a diagram to make this clearer.

Pie chart showing how many people had hair loss and whether they needed a wig

Pie chart showing how many people had hair loss and whether they needed a wig
Pie chart showing how many people had hair loss and whether they needed a wig

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The person also wants to know about the possible side effects of the drug and how many people are affected.

The doctor tells them that side effects included:

  • headaches
  • feeling tired
  • a sore throat.

Of the 100 people in the study:

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

Some people had rarer side effects:

  • 1 person had an allergic reaction = 1%
  • 2 people had very itchy skin = 2%
  • 4 people had pain in their stomach = 4%.

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

Bar chart showing the possible side effects of the drug and how many people were affected

Bar chart showing the possible side effects of the drug and how many people were affected
Bar chart showing the possible side effects of the drug and how many people were affected

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The person also wants to know more about how people’s lives were affected by the side effects. The doctor tells them:

  • Of the 100 people who took the new drug, most (72 people) had mild or no side effects.
  • 23 people had side effects that affected their day-to-day lives.
  • Only 5 people had side effects so severe that they had to stop taking the medicine. The person who had the allergic reaction and the people who had a stomach ache did not have the drug again.

This information can be shown in a ‘smiley face’ diagram.

‘Smiley face’ diagram showing how people’s lives were affected by the side effects
‘Smiley face’ diagram showing how people’s lives were affected by the side effects

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There are many different ways of showing information. Remember that it is fine to ask for explanations to be repeated if there is something you do not understand.


Benefit

A benefit is something good or helpful that happens as a result of doing (or not doing) something. For example, a benefit of a healthy diet is that you are less likely to be overweight and 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 does not 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 the result of 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 does not know anyone who has had it. These experiences can influence your behaviour and may make you less likely to have chemotherapy.

In this example, it is 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%
  • 25 in 100
  • 0.25
  • ¼

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 at some point in your life 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 the following:

  • You have a 6 in 100 (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 (6%) to 3 in 100 (3%).

The reduction in risk can be described as the following:

  • 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. It is used more often to describe how effective a treatment is.

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 are 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.