Descriptive epidemiological study of rare, less common and common cancers in Western Australia

Abstract

Background There are no epidemiological studies describing rare cancers in Western Australia (WA). We aimed to fill this gap by estimating the incidence and five-year survival of rare, less common and common cancers in WA, based on definitions for rarity used by the Australian Institute of Health and Welfare and cancer groupings from the project on Surveillance of Rare Cancers in Europe (RARECARE). This research will enable policy- and decision-makers to better understand the size and nature of the public health problem presented by rare cancers in WA. It is anticipated that this study will inform improved health service design and delivery for all WA cancer patients, but particularly those with rare and less common cancers. Methods We estimated incidence and five-year survival rates of rare, less common and common cancers in WA using data sourced from the WA Cancer Registry for the 2013–2017 period. Cancers were defined as rare (< 6), less common (6–12), or common (> 12) based on their crude incidence rate per 100,000 people per year. Results Rare cancers make up 21.5% of all cancer diagnoses in WA, with a significantly poorer five-year survival of 58.2% (95% confidence interval (CI) 57.3–59.1%), compared to patients diagnosed with a common cancer, whose five-year survival was 87.8% (95% CI 87.3–88.3%). Survival for less common cancers was significantly poorer than both rare and common cancers, at 48.1% (95% CI 47.3–49.0%). Together, rare and less common cancers represent 48.4% of all cancer diagnoses in WA. Conclusions While rare cancers are individually scarce, collectively over one in five cancer patients in WA are diagnosed with a rare cancer. These patients experience significantly worse prognoses compared to patients with common cancers.

Geographical and spatial disparities in the incidence and survival of rare cancers in Australia

“…While the definition of rare cancers varies, our estimate of around 22% of all cancers being rare cancer types is consistent with other Australian (17%-22%) 6,36 and international (15%-24%) studies. 2,3,5,14,15,37 Although international comparisons regarding survival should be made cautiously, given that there are likely to be differences in the case mix of individual cancer types categorised as rare cancers, our 5-year relative survival estimates (51%-56%) were in the same range as estimates for the United States, 2,8 Central and Northern Europe 4,5 and better than the combined estimate for Europe of around 48%.…”

“…A reliable epidemiological description of rare cancers requires a low proportion of cases detected by death certificates only and those with NOS morphology. Both these data quality indicators for our study were at the lower end of international standards 1,6,8 While we cannot test the possibility that excluded cases may have impacted geographical differences, given their low numbers this is considered unlikely.…”

“…48 In our study, around 3% of all cancer cases from Australian cancer registries could not be assigned a Tier-1 cancer entity, in addition to around 6% that could be assigned a Tier-1 but not Tier-2 cancer entity. However, several studies have validated the use of the RARECANCER list in describing rare cancer epidemiology in non-European settings, 2,6,14,15 and its use enables international comparisons. 8,14 Overall, around 7% of all cases in the initial cohort had NOS morphology codes, meaning they could not be assigned to a specific (rare) cancer Tier-2 entity.…”

“…All cancers were classified using a list of clinically relevant and histologically defined cancer types (RARECARE list), 8 developed by the European RARECARE consortium, chosen here to allow comparisons with international studies 8,14 and the only previous study on rare cancers epidemiology from Australia. 6 The RARECARE list divides cancers according to their combined International Classification of Diseases for Oncology third edition, (ICD-O3) site (topography) and morphology codes into two tiers. The first (Tier-1) comprises major cancer entities in a clinical sense (eg, "soft tissue sarcoma") that direct patient referral policies while the second (Tier-2) categorises Tier-1 types into clinically distinct tumours (eg, "soft tissue sarcoma of limb").…”

“…Rare cancers are a heterogenous group of diseases which, while individually uncommon, 1 collectively represent a substantial cancer burden 2 , 3 , 4 ; comprising around a quarter of all cancers diagnosed in the United States, 2 Europe 3 , 5 and Australia. 6 Despite their high collective occurrence, research on the epidemiology and aetiology of individual rare cancer types can be challenging, 7 although risk factors commonly reported for rare cancers include smoking, alcohol, obesity, infectious agents, and occupational carcinogens. 8 , 9 , 10 In addition, clinical trials, effective treatment options and evidence‐based guidelines for their management are limited.…”