# Age and Cancer

Author: T M Mills

Older people are more likely to be diagnosed with cancer than younger people.
According to a recent report from the Australian Institute of Health and Welfare1, “The incidence of cancer is expected to increase with age”. One finds similar statements in many publications on cancer statistics.

In other words, the incidence rate of cancer is associated with the age of the population.

This association can be illustrated vividly with a simple diagram.

Table: Age and cancer in LGAs in Victoria
The incidence rate of cancer in a population is strongly associated with the median age of the population.

The incidence of cancer is defined to be the number of new cases diagnosed in a particular region and a particular year. The incidence rate is the number of new cases per 100,000 head of population.

Now cancer is a notifiable disease in Australia, as in some other countries. All new cases of cancer, except for certain skin cancers, must be reported to the cancer registry in the state. Hence Australia has high quality data on the incidence of cancer that has been collected over many years. Much of the data are freely available on-line from the Australian Institute of Health and Welfare.

In Australia, a Local Government Area (LGA) is a defined region associated with some form of local government such as a city council, or shire council. In the state of Victoria in Australia, there are 79 LGAs.

Figure 1 is a scatter diagram. There is one data point for each LGA in Victoria. On the vertical axis is an estimate of the average incidence rate of all cancers combined for the five year period 2006-2010 in an LGA.

This was calculated as the average incidence in the LGA for 2006-2010, per 100,000 head of population of the LGA in 2008. The incidence data were provided by Victorian Cancer Registry.

On the horizontal axis is the estimated median age of the population of the LGA in 2008. These estimates were calculated from population data available from the Australian Bureau of Statistics2.

The scatter diagram illustrates the strong association between the incidence rate of cancer in a population and the median age of the population. Spearman’s coefficient of correlation was r=.93, p<0.01.

I thank Victorian Cancer Registry, Cancer Council Victoria for providing the data on the incidence of cancer.

## References

• 1. Australian Institute of Health and Welfare & Australasian Association of Cancer Registries. Cancer in Australia: an overview, 2012. Cancer series no. 74. Cat. no. CAN 70. Canberra: AIHW; 2012.
• 2. Australian Bureau of Statistics. Population Estimates by Age and Sex, Australia by Geographical Classification [ASGC 2011], 2001 to 2011. Canberra: ABS, 2011. ABS Cat. No. 3235.0. (accessed Apr 2013).

### T.M. Mills

Quote:

This study is showing that the more older you get, the more likely it is for you to get cancer. one particular issue with this statistic is that why is it more common between the ages 30-50?

Dear Stella, Thank you for the question. The x-axis measures the median age of the people in the local government area. It does not represent the age of individuals. I hope that this clarifies matters.

### T.M. Mills

Quote:

Is there an association between the location and other areas where cancer rates are skyrocketing? The rate keeps going up. Is this due to population growth, or something other? can someone explain these numbers?

Dear Yudi, Thank you for the interesting question. One inference to draw from the graph is that cancer is associated with age. A major factor in explaining increasing cancer rates is that populations are ageing. Not only do you and I get a year older each year - but the average age in the entire population is increasing. If you ask "Why is there so much dementia around these days?" people will say "It's because we are living longer and the population is ageing". To a large extent, the same is true of cancer. Of course, sadly some people get cancer when they are young. But by and large cancer tends to affect older people more than younger people. By itself, age does not cause cancer. It is just one major factor that helps us to understand the increasing incidence of the disease.

### T.M. Mills

Quote:

This study is showing that the more older you get, the more likely it is for you to get cancer. one particular issue with this statistic is that why is it more common between the ages 30-50?

Dear Stella, Thank you for reading the article and making a comment. The x-axis indicates the median age of the population in the local government area. In all local government areas, the median age is between 30 and 50 approximately. For example, in my city, the median age is about 45 years old. The diagram shows that the incidence rate of cancer increases with the median age of the population. Older populations experience more cancer. I hope that this clarifies the meaning of the diagram for you.

### Yudi Sahler

Is there an association between the location and other areas where cancer rates are skyrocketing? The rate keeps going up. Is this due to population growth, or something other? can someone explain these numbers?

### Stella Aning

This study is showing that the more older you get, the more likely it is for you to get cancer. one particular issue with this statistic is that why is it more common between the ages 30-50?

### T.M. Mills

Quote:

Why is there only one data point over the age of 50 years? Does this reduce the strength of correlation over this age?

Thank you for the comment. Each point represents one Local Government Area. There is only one LGA in Victoria where the median age is over 50 years.

### A Nel

Why is there only one data point over the age of 50 years? Does this reduce the strength of correlation over this age?

### T.M. Mills

Quote:

While correlation is evident, does this have any scientific explanation? Without that this would be more of an mathematical exercise.

Thank you for the comment. The purpose of the diagram is simply to illustrate the fact that "age" is associated with being diagnosed with cancer. People often ask "Why is there so much cancer these days?" A partial explanation is that age is a risk factor associated with cancer. This can be illustrated in many ways; the diagram in this article is one way.

### Subramaniam P G

While correlation is evident, does this have any scientific explanation? Without that this would be more of an mathematical exercise.

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