Cancer is among the leading causes of death in Australia. As far too many of us know, its impact on individuals and communities can be devastating. But how does cancer affect Australia overall?
To find out, The Conversation visualised a rich data set from the Cancer in Australia report produced annually by the Australian Institute of Health and Welfare (AIHW). We asked two experts – Cancer Council Victoria’s Dallas English and Brigid Lynch – to reflect on the picture that emerged.
Here’s what we found.
Cancer mortality rates are declining overall
We’ll start with the good news: although the cancer incidence rate has increased by just over a quarter since 1982, the mortality rate has gone down. That’s reflected in the falling mortality-to-incidence ratio.
The incidence rate is the number of new cases in a given period (relative to the size of the population). The mortality rate due to cancer is the number of deaths that occurred in a given period for which the underlying cause of death was recorded as cancer.
The mortality-to-incidence ratio is not really the same as a “survival rate” but is sometimes used as a proxy for one.
“So for example, if you look at mortality in 2013 and incidence in the same year, you would see people dying in that year who were diagnosed some time earlier. But, generally, it is a good proxy for survival after diagnosis,” Professor English said.
The AIHW data visualised here show age-standardised cancer rates across a five year period leading up to 2013 (age standardised means the data were adjusted to account for the fact that some areas may have an older demographic, to remove the influence of age on the results). It’s a snapshot in time and depending on the size of the region and the type of cancer, things may look somewhat different in another time period.
Use the drop-down menus below to see how various cancer rates look across Australia:
Professor English said that some of the differences in cancer rates across the country are due to random variation but there are also some trends worth noting.
“Let’s take melanoma, for example. The map shows that if you live in Queensland and northern NSW, the rates are much higher than for people who live in the south, in places like Tasmania and Victoria,” he said.
For some areas, however, the pattern you see on the map reflect other factors. “For colorectal cancer, for example, the incidence and mortality rate looks low in the NT but that could be due to small populations there, spread across large areas,” he said.
The mortality-to-incidence ratio for all cancers mixes together cancers that have a poor survival rate (such as lung cancer) with others that have a better survival rate, he said.
Cancer rates in your area
Search for your postcode to see how cancer rates in your area look. Again, you can toggle between incidence rate, mortality rate and mortality-to-incidence ratio.
However, Professor Dallas English notes that “just because your area has a high cancer incidence or cancer mortality rate, it doesn’t imply you are living in a dangerous area.”
“It’s not as though you live in a cancer cluster. These rates are more determined by the lifestyle and genetic factors of people who live there.”
Remoteness and socioeconomic status
A stark picture emerges when you visualise the mortality-to-incidence ratio against socioeconomic status.
The AIHW report said that the age-standardised mortality rate for all cancers combined was highest among those living in the lowest socioeconomic group and lowest among those living in the highest socioeconomic group.
Associate Professor Brigid Lynch, a senior research fellow at Cancer Council Victoria said it’s very clear that socioeconomic position has a strong influence on cancer incidence and mortality in Australia.
“The better off people are, the less likely they are to develop most cancers – and they are more likely to survive after diagnosis,” she said.
“We know that socioeconomic position influences cancer in a number of ways including via health behaviours. But these don’t explain all of the influence.”
The AIHW reports that the age-standardised mortality rate of all cancers combined was higher for Indigenous Australians than for their non-Indigenous counterparts.
“For Indigenous populations in general, cancer survival is poor. Lower average socioeconomic status is part of that,” said Professor English. “You tend to have people being diagnosed at much more advanced stages of cancer and Indigenous Australians have, on average, poorer access to health services.”
“There have been a lot of studies showing that Australians in remote and regional areas have poorer survival than in big cities, regardless of indigeneity.”
For prostate cancer, the biggest effect on variation in incidence rates is the amount of prostate specific antigen (PSA) testing that goes on, he said, because this test is known to deliver a high rate of false positives.
Professor English also said that:
Breast cancer is more common among women of higher socioeconomic status. That may be linked to the fact that women with higher socioeconomic status tend to have fewer babies or have babies later in life. (The older a woman is when she has her first full-term pregnancy, the higher her risk of breast cancer.)
Lung cancer is associated with lower socioeconomic status, however it has a high mortality rate across the board.
The relationship between prostate cancer incidence and socioeconomic status is complicated. It’s important to remember that men who have a high income are more likely to get tested.