Understanding benefits, risk and cancer statistics

A benefit is something good or helpful that happens as a result of doing (or not doing) something. For example, a healthy diet benefits your health because you are less likely to be overweight. As a result, you reduce your risk of certain health conditions.

A benefit of cancer treatment may be that the cancer is cured or controlled, sometimes for many years. The cancer staying the same size, or growing at a slower rate for a time, can also be a benefit.

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.

You can show numbers in different ways. A doctor might describe risk using percentages (%), fractions or likelihood.

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

• 25%
• 25 out of 100
• 0.25
• ¼.

It can help to think about risk in both ways. For example:

• 25 out of 100 people had this side effect
• 75 out of 100 people did not have this side effect.

It can be difficult to understand how risk relates to you.

When describing risk, doctors sometimes talk about absolute risk and relative risk. Or you might read these terms in a research paper.

Ask your GP or cancer doctor if the numbers they give you are absolute or relative risk. If you are not sure about what a level of risk means, ask your GP, cancer doctor or specialist nurse to explain things in more detail.

The following examples explain the difference between absolute risk and relative risk.

This is just an example and does not refer to any real medicine or research.

The doctor tells someone the following:

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

The reduction in risk can be described in 2 different ways.

The absolute risk of developing the disease without drug X is 6%. But with drug X it is 3%. The absolute risk reduction is 3% (6 minus 3).

When deciding on a treatment, you and your cancer doctor could talk about whether the reduction in absolute risk outweighs the overall risks and side-effects.

The risk has dropped from 6% to 3%. It is now half as large as it was. Because a half can also be described as 50%, the risk has been reduced by 50%. This is the relative risk reduction.

If you hear that a drug or treatment reduces your risk by 50%, you would probably be very interested. You may feel differently to hear that it reduces your absolute risk by 3%.

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

It is important to talk to your team about both types of risk and what this means for your situation.

It can be difficult to think about how statistics relate to you as an individual and which percentage group you are likely to be in. You can talk to your cancer doctor or specialist nurse and ask for their advice on your situation.

We have more information about making treatment decisions.

The following example shows how information can be presented in different ways. This is an imaginary example. It does not refer to any real drug or research. It shows that when making treatment decisions it is important to think about both:

• how effective a treatment is
• its possible side effects.

Example: A cancer doctor talks to someone who is going to start chemotherapy about a new drug which may help to prevent hair loss. Before taking the drug, the person wants to know how well the drug works. Of 100 people who took the new drug:

• 10 people had no hair loss (10%)
• 23 people had a little hair loss (23%)
• 37 people had a lot of hair loss (37%)
• 30 people had total hair loss (30%).

The new drug slowed down or stopped total hair loss for 70 people (10+23+37). But 67 of the 100 people who took the drug had a lot of or total hair loss (37+30).

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

Pie chart showing how many people had hair loss and how much hair loss they had

The person now has an idea of how effective this drug is. But they also need to know its possible side effects 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 more than 1 side effect.

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

The person also wants to know how people’s lives were affected by the side effects. The doctor tells of the 100 people who took the new drug:

• 72 people had mild side effects or no side effects (72%)
• 23 people had side effects that affected their day-to-day lives (23%)
• Only 5 people had side effects so severe they had to stop taking the drug (5%).

This information can be shown in an emoji (smiley face) diagram.

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