When people notice that several people they know have been diagnosed with cancer, it can sometimes feel like these cases might be connected. People often worry that a number of cases of cancer have been caused by the same thing. They suspect what researchers call a ‘cancer cluster’.
What are cancer clusters?
A cancer cluster occurs when more cases of cancer than expected are diagnosed in a group of people, living in a certain area over a short period of time.
An example of a ‘real’ cancer cluster (one with a definite cause) happened in the 1960s, when scientists linked cases of mesothelioma – a rare cancer – with exposure to asbestos fibres. When many cases of mesothelioma emerged in people living near asbestos mines, scientists thought there could be a link between inhaling asbestos fibres and cancer.
Further research confirmed this link and showed that working with asbestos is the major risk factor for developing mesothelioma. Asbestos is now banned in the UK. You can read more about asbestos and cancer on our workplace webpages.
Although ‘real’ cancer clusters do occur, most suspected clusters are due to chance. And it can be quite difficult to tell the difference between the two.
'Real' Cancer Clusters
‘Real’ cancer clusters are rare, but there are some things that help experts identify groups of cancer cases that share a common cause:
- They involve more cases of cancer than expected within a small geographical area
- There are many cases of a single type of cancer (or of similar types of cancer), rather than cases of different cancer types
- The cancer type is rare
- The cases are affecting age groups that would not normally be associated with this type of cancer
Suspected Cancer Clusters
There are a number of possible reasons why people might suspect a cancer cluster:
- Cancer is a very common disease. More than 1 in 2 people will develop some form of cancer in their lifetime, a number which is on course to keep rising. This is partly because of our increasing life expectancy
- The risk of cancer increases with age. Sadly, this means that the older we get, the more likely it is that we will know more people with cancer
- Even if cancer cases occur randomly in the population, some areas will have more cases than others due to chance. This can make it seem like there is a cancer cluster, when in fact it is normal for numbers of cancer cases to vary between areas
- When people have had a personal experience of cancer or know someone who has been diagnosed, it’s natural to want to find out what caused the disease. We might then become more aware of other people around us who have also developed cancer, and think that these cancers may be linked
What should I do if I’m concerned about a cluster?
If you’re concerned about an unusual number of cancer cases in your area, you should contact your local public health authority. They will be able to decide whether an analysis of the reported cluster is needed. If you’d like to find out more about investigations of cancer clusters, you can read the Standard Operating Procedure by the United Kingdom and Ireland Association of Cancer Registries (UKIACR).
If you are concerned about a possible cluster of cancer cases in your workplace then you should contact the Health and Safety Executive (HSE). The HSE is the national regulator for health and safety in the workplace.