Exploring variations in ovarian cancer survival by age and stage (ICBP SurvMark-2): A population-based study
Introduction
Ovarian cancer is the 8th most common cancer (excluding easily treatable, non-melanoma skin cancer) and the 5th leading cause of cancer death among women in high-income countries [1]. While incidence rates have decreased across most high-income countries over the past three decades, mortality rates declined in a slower pace [2]. Ovarian cancer symptoms are non-specific and early stage ovarian cancer is often asymptomatic. Several early detection methods have been introduced for ovarian cancer, however, currently screening is not feasible due to the low sensitivity and specificity of available tests [3]. Chemotherapy regimens for ovarian cancer have evolved with recent advances including the introduction of anti-angiogenic therapy and the use of targeted therapies such as poly(adenosine-diphosphate ribose) polymerase (PARP) inhibitors [4].
Previous large population-based studies have reported substantial differences in ovarian cancer survival between high-income countries [5,6]. There are many complex factors that impact cancer survival, including age and stage at diagnosis, as well as availability of diagnostic resources and access to optimal treatments [5,7]. A previous study by the International Cancer Benchmarking Partnership (ICBP) showed that more than half of all ovarian cancer cases occurred in women older than 65 years, and the majority of women were diagnosed with advanced stage disease [8]. Thus, understanding stage distribution as well as survival by stage as it relates to age at ovarian cancer diagnosis is essential to inform improvements in policy and practice.
This study evaluates the differences in survival by age and stage at diagnosis within and across seven high-income countries. The ICBP is a collaboration of population-based cancer registries, clinicians, researchers, and policymakers from countries with similar cancer registry coverage, national health system expenditure and universal access to healthcare. Using the most up-to-date, real-world data, the ICBP investigates international differences in cancer survival in order to identify areas where practice can be improved through evidence-based recommendations.
Section snippets
Study population
Detailed description of the data collection and processing in the ICBP SurvMark-2 project was previously described by Arnold and colleagues [9]. Data for ovarian cancer cases were obtained from 21 population-based cancer registries (PBCRs). These included Australia (New South Wales (NSW), Victoria, and Western Australia), Canada (Alberta, British Columbia, Manitoba, New Brunswick, Newfoundland, Nova Scotia, Ontario, Prince Edward Island, Quebec, and Saskatchewan), Denmark, Ireland, New Zealand,
Statistical analysis
Survival by TNM and FIGO stage was calculated for Canada, Denmark, Ireland, and the UK. FIGO staging data with sub-categories was prioritized over individualized TNM clinical and pathological information for TNM stage. Nodal involvement coded as “NX” was assumed to be N0, and metastasis coded as “MX” was assumed to be M0. In the current study, stage I-IV was used to refer to TNM or FIGO stage.
Supplementary Fig. S4 illustrates the process to harmonize stage for ovarian cancer. Australia and New
Patients' characteristics including cancer stage by country
The median age at diagnosis ranged from 63 years in Canada to 67 years in Denmark and UK (Table 1). The proportion of cases with unknown stage was smallest in Canada (TNM = 3.6%; SEER = 3.0%) and largest in the UK (TNM = 27.4%; SEER = 27.1%). There were minimal differences in the stage distribution before and after unknown stage at diagnosis was imputed. The largest proportion of cases were diagnosed at advanced stage, and variations between countries were minor for both TNM stage, as well as,
Discussion
This study presents the most up-to-date estimates of all-ages, stage-specific and age-specific 1-year and 3-year NS for ovarian cancer across seven high-income countries. NS was highest in Norway, Australia, and Denmark followed by Canada, whereas the UK, New Zealand and Ireland exhibited lower NS. Survival differences between countries were most pronounced in older women and women with ‘distant’ stage disease. The latter represents the majority of ovarian cancer cases. Consequently, the
Conclusion
Our study highlights existing international survival differences amongst women diagnosed with ovarian cancer in seven high-income countries. The findings showed that survival differences between countries were most pronounced for older women and women with advanced disease at diagnosis. Survival variations between countries are suggestive of differences in access to and quality of care, adherence to national and international guidelines, differences in surgical philosophy and treatment
CRediT authorship contribution statement
Citadel J. Cabasag: Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Writing - original draft, Visualization. John Butler: Writing - review & editing. Melina Arnold: Methodology, Data curation, Writing - review & editing, Visualization, Project administration. Mark Rutherford: Methodology, Software, Formal analysis, Visualization. Aude Bardot: Data curation. Jacques Ferlay: Data curation. Eileen Morgan: Writing - review & editing. Bjørn Møller: Writing - review
Declaration of competing interest
None of the authors have any potential conflicts (financial, professional, or personal) related to the manuscript to disclose.
Acknowledgements
The ICBP is funded by the Canadian Partnership Against Cancer; Cancer Council Victoria; Cancer Institute New South Wales; Cancer Research UK; Danish Cancer Society; National Cancer Registry Ireland; The Cancer Society of New Zealand; NHS England; Norwegian Cancer Society; Public Health Agency Northern Ireland on behalf of the Northern Ireland Cancer Registry; DG Health and Social Care, Scottish Government; Western Australia Department of Health; Public Health Wales NHS Trust. The authors would
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