Incidence, survival and mortality
This page explains incidence, prevalence, survival and mortality statistics. These are the most common groups of statistics produced about cancer. And they mean very different things. There is information about
Incidence means how many people get a particular type of cancer every year. It is often written as the number of cancer cases per 100,000 people in the general population. These calculations are done for every type of cancer.
For example, in the UK in 2011 there were
- 49,936 women diagnosed with breast cancer – about 155 cases per 100,000 women
- 23,770 men diagnosed with lung cancer – about 77 cases per 100,000 men
- 2,207 men diagnosed with testicular cancer – about 7 cases per 100,000 men
Non melanoma skin cancer is the most commonly diagnosed cancer overall, with around 100,000 new cases registered in 2011. Nearly all these people are cured. Non melanoma skin cancer is often excluded from cancer incidence statistics because it is very common and can usually be easily treated.
Other ways of looking at incidence include
- Incidence in different age groups
- Incidence in different countries
If we take the UK population as a whole, we can see that the number of people getting different types of cancer varies between different groups.
Cancer incidence means the number of people newly diagnosed with cancer within a given period of time.
Incidence can vary by age as well as other factors. Although there are variations for specific cancers, the number of cancers diagnosed generally increases with age. Nearly two thirds of cancers (63%) are diagnosed in people aged 65 and over.
Overall, prostate cancer is the most common cancer in men – 25 out of every 100 male cancers (25%) are prostate cancer. It is most common in older men and only 1 out of 100 (1%) occur in men under the age of 50. But other cancers are more common in younger age groups. For men aged 25 to 49, testicular cancer is the most common. Prostate cancer only accounts for 4% of male cancers in this age group.
Breast cancer is the most common cancer in women – 31 out of every 100 cancers (31%) diagnosed in women are breast cancer. But in women aged 15 to 24, melanoma and Hodgkin lymphoma are the most common (16% each), with only a few women diagnosed with breast cancer in this age group.
If you look at cancers diagnosed in children under 15 years old then leukaemia is the most common cancer. 1 in 3 cancers (33%) in this age group are leukaemia.
The rates of particular cancers are often different in different countries. This is interesting because it could help us discover more about the causes of different cancers. Breast cancer incidence is often quoted as an example of this.
The incidence of breast cancer in Japan is much lower than in the USA or the UK. But the incidence of breast cancer in Japanese women living in the USA is the same as for the general population of American women. To doctors and researchers, this implies that the causes of breast cancer are probably more closely related to life style and the environment than they are to our genetic make up.
Cancer prevalence means the number of people in the population who have had a diagnosis of cancer.
Some of these people will have been diagnosed some time ago and may have been cured or are cancer free. Other people may have been diagnosed more recently. So prevalence means all the people who have a type of cancer at a particular time. This is different to incidence, which means all the new people who get a type of cancer during a particular period of time.
Cancer prevalence depends on how many people get the cancer (incidence) and how long people live after they are diagnosed (survival). So the most prevalent types of cancer are the most common cancers which have the highest survival rates. For example, in the UK in 2006, the most prevalent cancer in men was prostate cancer, and around 181,000 men were still alive up to 10 years after being diagnosed.
Survival statistics for cancer are usually written as 5 year survival or 10 year survival. For some cancers they may be written as 1 year or 2 year survival. These statistics can sometimes be difficult to understand.
5 year survival means the percentage of patients who are alive 5 years after their diagnosis. It doesn't mean that these people lived for exactly 5 years and then died. It doesn't mean that they were all cured either. Some of these people will be cured and the cancer will never come back. For some people the cancer may have come back and they are living with it. In some people the cancer may come back after the 5 year period.
Everyone who has a particular type of cancer is usually included in the statistics for that cancer. Straight forward 5 year survival figures are very general. They include everyone with that type of cancer, at all stages and grades.
You may come across 5 year survival figures by stage of cancer. These may be simplified into groups such as
- Local disease (cancer that has stayed in the area where is was diagnosed)
- Metastatic disease (cancer that has spread to another part of the body)
Or the statistics may be divided by the stage of the cancer, such as statistics for
- Stage 1 cancer (small and localised)
- Stage 2 cancer (larger but localised)
- Stage 3 cancer (spread into surrounding tissues or lymph nodes)
- Stage 4 cancer (spread to other parts of the body)
You can read about cancer staging.
Sometimes disease free survival figures are used. This means everyone with that type of cancer who is alive and well (without a recurrence of their cancer) 5 years after diagnosis.
Mortality means the number of people who have died.
Mortality figures for cancer need to be looked at alongside incidence figures and other statistics. They are used as a general guide to what is happening in the diagnosis and treatment of diseases. Some cancer mortality statistics may not take account of the stage, grade or any specific sub type of a cancer.
It is important to remember that statistics are very general. You may read that 49,936 women were diagnosed with breast cancer in the UK in 2011 and 11,643 women died in that year. Almost all of the women who died would have been diagnosed some years before. In a lot of cases, they would have lived for many years after their cancer diagnosis.
Changes in mortality figures over time are difficult to interpret. The incidence of a cancer may be falling, so less people die from it. Or treatment may be improving so that more people are cured. Treatment improvements may sometimes mean that more people live longer after they are diagnosed. This will make mortality figures fall in the short term.
The last type of statistics to cover are those about the risk of getting any particular type of cancer. This is often written as life time risk. Using the available figures, statisticians work out the risk of any one of us getting a certain type of cancer at some point during our lives.
This figure is sometimes written as a proportion: for example, the calculated life time risk of lung cancer for a man in the UK is 1 in 14. This means that out of every 14 men in the UK, one will get lung cancer at some point in his life (and 13 won't).
To change this to a percentage, you divide it into 100. 100 divided by 14 equals 7. So the percentage life time risk of lung cancer for a man in the UK is 7%. But this is the overall risk. The risk may be higher or lower, depending on particular factors such as whether a person smokes or not.
Lifetime risk is a cumulative risk. This means that the risk adds up as you get older. So the risk for an average 45 year old person is not 1 in 14 – it will be much lower.
Cancer risk statistics can't help us to identify who will get particular cancers. But they can sometime help us to know who may have a higher risk than other people in the general population. These figures are produced to help people who study the incidence of disease (epidemiologists) and people who work out how much money we need to spend on health care (health economists).
These statistics are important because they tell us the most important health problems of our time. And from that, we can work out the areas where we need to concentrate spending on research, screening, treatment and training.
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