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AUSTRALIAN CANCER ATLAS 2.0 – Technical report

3 Overview of approach

3.1 Indicators

The average ‘cancer burden’ is measured in the Australian Cancer Atlas by the following six separate indicators: diagnosis, survival, clinical characteristics, screening or testing, cancer risk factors and interventional treatments for prostate cancer.

3.1.1 Cancer diagnosis

The term “cancer diagnosis” refers to the number of new cancer cases identified in a specific area during a certain time. Only looking at geographical variation in the number of diagnoses can be misleading because some areas have higher populations than others. To give a more accurate picture, we focus on differences in cancer diagnosis rates. These rates are calculated by dividing the number of new cancer cases in an area by the total population of that area.

Information about diagnosed cancers in Australia and how well people are doing after diagnosis comes from the Australian Cancer Database. (Australian Cancer Database) This database is managed by the Australian Institute of Health and Welfare. The Cancer Data & Monitoring Unit brings together data from each of the eight state and territory cancer registries in Australia to create the Australian Cancer Database.

When the Australian Cancer Atlas talks about cancer diagnosis, it is referring to those cancers diagnosed among Australians aged 15 and older.

3.1.2 Cancer survival

The term “cancer survival” refers to how many people diagnosed with cancer are still alive a certain number of years after their diagnosis. In the Australian Cancer Atlas, we report survival five years after the initial diagnosis.

In the context of the Australian Cancer Atlas, we are particularly interested in survival related to the cancer itself, rather than other causes such as injury or dementia. However, finding the exact cause of death can be tricky, especially when someone has multiple health issues at the same time. This makes it hard to calculate “cause-specific survival” because we do not know the single cause of death.

One way to deal with this is to use “relative survival”, where we compare the overall survival of a group of cancer patients with the overall survival of the general population. We match the comparison by age group, so any difference in survival between the two groups can be linked to the cancer diagnosis.

If the 5-year relative survival estimate is 100%, it means that, on average, there’s no difference in survival between the cancer patients and the general population over the five years following the diagnosis. On the other hand, a 5-year relative survival estimate of 50% indicates that, on average, the group of cancer patients is about half as likely to survive for five years as we would expect in the general population.

3.1.3 Cancer clinical characteristics

An invasive cancer means it has spread beyond the cells where it first started and has the potential to invade nearby tissues and organs. These are the cancers usually reported by cancer registries in Australia. The Australian Cancer Atlas provides details about the geographical patterns for around 30 different invasive cancer types.

In situ cancers are found when they are still confined to the original tissue and have not spread. In Australia, registries usually only collect and report on in situ cancers for melanoma and female breast cancer, both of which are included in the Atlas.

The stage at which cancer is diagnosed shows how far it has spread. For invasive cancers, there are typically four stage categories, with stage 1 being localised and stage 4 being more widespread (stage 0 is in situ cancers). Generally, the higher the stage, the more severe the cancer and the worse the chances of survival. In Australia, data on the stage at diagnosis for certain cancers are only available for the whole country in 2011. Melanoma, breast cancer, and prostate cancer were the only ones considered complete enough for reporting in the Australian Cancer Atlas.

For melanoma, the thickness of the tumour also indicates how severe it is. The Atlas includes information on thickness for melanomas diagnosed from 2010 to 2019, categorised as thin (≤1mm) or thick (>1mm).

3.1.4 Cancer screening or testing

The Australian Cancer Atlas includes information on breast cancer screening, cervical screening, and bowel cancer screening, each of which are formal screening programs within Australia. In addition, there are estimates for prostate-specific antigen (PSA) testing, which is an ad-hoc method for detecting signs of prostate cancer.

3.1.4.1 Bowel cancer screening

Regular screening has been shown to lower both the number of new cases and deaths from bowel (or colorectal) cancer. It helps by finding and treating pre-cancerous issues and early-stage cancer.

In Australia, the government runs the National Bowel Cancer Screening Program, (NBCSP, National Bowel Cancer Screening Program) providing free screening every two years. They use a test called the immunochemical faecal occult blood test (iFOBT). The test checks for blood in the stool, which is an early sign of bowel cancer. The bowel screening program is for Australians aged 50 to 74. The goal is to detect signs of bowel cancer early and reduce related deaths. (Australian Institute of Health and Welfare, 2023a) Eligible Australians in this age group receive a free test to use at home. Publicly available population-level participation data for persons in the National Bowel Cancer Screening Program from 2019 to 2020 were obtained from the Australian Institute of Health and Welfare. Note that bowel cancer screening carried out outside the program are not included in these bowel cancer screening data.

3.1.4.2 Breast cancer screening

Early detection of breast cancer is important as it enables more effective treatment thus improving survival outcomes. The BreastScreen Australia program (BreastScreen Australia) invites women aged between 50 to 74 years to have a free mammogram every two years. The goal is to reduce illness and death from breast cancer using screening mammography to detect unsuspected breast cancer in women. (Australian Institute of Health and Welfare, 2023b) Breast screen Australia participation data for females from 2019 to 2020 were obtained from the Australian Institute of Health and Welfare. Note that mammograms carried out through private facilities are not included in these breast screening data.

3.1.4.3 Cervical screening

Regular screening has been shown to lower both the number of new cases and deaths from cervical cancer. It helps by finding and treating pre-cancerous abnormalities.

In Australia, the government runs the National Cervical Screening Program, (NCSP, National Cervical Screening Program) providing free screening every five years. The cervical screening test looks for signs of the human papillomavirus (HPV) which is a common infection that causes most cervical cancers. Women aged 25 to 74 years of age are invited to have a cervical screening test every five years through their healthcare provider. Samples for testing may either be self-collected or collected through a health care provider. The goal is to detect abnormalities early for monitoring and if needed treatment before potential development of cervical cancer. (Australian Institute of Health and Welfare, 2023c) Publicly available population-level participation data for the National Cervical Screening Program between 2018 and 2022 was obtained from the Australian Institute of Health and Welfare. Data was available on both the number of eligible females who had a screening HPV test and those who had a cervical test for any reason. The second measure is deemed to be a better indicator of overall participation in cervical screening and was used for Atlas 2.0. (Australian Institute of Health and Welfare, 2023c)

3.1.4.4 PSA testing

PSA is a protein produced by the prostate – a small gland below the bladder of men.

Regular testing for PSA is commonly used as an opportunistic approach to check asymptomatic men for potential prostate cancer risk. However, this test has a low positive predictive value, making it challenging to distinguish between cancerous and non-cancerous conditions in the prostate. As a result, in Australia it is conducted on a case-by-case basis rather than being part of organised population-wide screening programs. This is different to the formal cancer screening programs in Australia for breast cancer, bowel cancer and cervical cancer.

The Australian Cancer Atlas reports geographical variation in PSA testing among males aged 50 to 79 from 2017 to 2018. The data about PSA testing came from the Medicare Benefits Schedule. (MBS) This data was provided by the Commonwealth Department of Health for item number 66655, which refers to checking for prostate issues in men who do not have symptoms.

3.1.5 Cancer risk factors

In Australia, at least one in three cancers can be linked to things we can change, like our lifestyle choices. (Whiteman et al., 2015) The Australian Cancer Atlas focused on five broad groups of factors that can increase cancer risk: smoking, alcohol, diet, weight, and physical activity (eight corresponding measures). We picked these after consulting a wide range of experts and looking at evidence from studies that showed connections to cancer.

The Atlas includes the following eight measures of risk factors, for persons:

3.1.6 Treatment

The Australian Cancer Atlas report geographical patterns of three different interventional prostate cancer treatments: radical prostatectomy, high dose rate brachytherapy and low dose rate brachytherapy. While there are other types of treatment for prostate cancer, data for every instance of these three treatments were available.

Radical prostatectomy involves removing part of or all the prostate and is common for localised or locally advanced prostate cancer.

Brachytherapy, a type of radiotherapy, implants a radioactive source near or inside the cancer to target cancer cells while minimising exposure to surrounding tissues. High dose rate brachytherapy releases a strong dose of radiation in short sessions, while low dose rate brachytherapy releases a lower dose over a more extended period.

Hospital admission data for any of the three treatments were extracted from the National Hospital Morbidity Database (NHMD) maintained by the Australian Institute of Health and Welfare.

3.2 Estimates by sex

Many of the measures included in the Australian Cancer Atlas are reported separately for males, females, and persons. The information about a person’s sex was sourced from the original data custodians.

Several cancer types are sex specific, such as prostate cancer and testicular cancer (only diagnosed among males) and cervical cancer, ovarian cancer, uterine cancer and vulval cancer (only diagnosed among females). While breast cancers can be diagnosed among males and females, due to the very low numbers of breast cancers diagnosed among males, the Australian Cancer Atlas only reports information about breast cancer among females.

In addition, some indicators are only provided for persons (for example each of the cancer risk factors, and bowel cancer screening) due to data availability.

3.3 Types of measures

The Australian Cancer Atlas shows how cancer varies relative to the Australian average (“relative”), as modelled counts (“absolute”, such as the number of cancers diagnosed, number of people screened) or both.

Absolute measures are only available when selecting the “Geographical patterns (average)” option.

Note that the absolute measures reflect estimates generated from the statistical models; there are no original count data reported at the small area level within the Australian Cancer Atlas.

3.4 Types of estimates

In the Australian Cancer Atlas, you will find three types of estimates displayed on maps, but the available types vary for each health indicator. For instance, for cancer diagnoses, cancer survival and treatment, you can see all three estimates, while for cancer risk factors, screening or testing, only Geographical patterns (average) is accessible.

3.4.1 Geographical patterns (average)

Geographical patterns (average) provide a snapshot of geographical patterns for the latest available time period (up to 10 years). Information is available for both relative estimates (compared to the Australian average) or absolute modelled counts (such as the number of cancers diagnosed).

3.4.2 Geographical patterns (separate time periods)

Geographical patterns (separate time periods) show how geographical patterns across Australia have changed over different time periods (typically, but not always, single years). This is available for relative estimates only, where area-specific rates for each time period are compared to the Australian average for that time period.

3.4.3 Changes over time for each geographical area

Changes over time for each geographical area show how the rates for each geographical area have changed over a combined time period. This is also available for relative estimates only, where the area-specific rates for each time period are compared to the Australian average over the combined time period. These changes reflect the national trends over time in many cases.