Trends in incidence and survival for anal cancer in New South Wales, Australia, 1972–2009
Introduction
The incidence of anal cancer, a rare digestive tract malignant tumour located primarily in the anal canal, is strongly associated with exposure to oncogenic types of human papillomavirus [1]. Reported increases in incidence worldwide have led to greater clarity on the role that HPV plays in anal cancer aetiology including population subgroups at increased risk of disease [2], [3], [4], specifically that the aetiology of anal cancer is closer to that of other genital cancers compared to gastrointestinal malignancies. The most common histological subtype of anal cancer is anal squamous cell carcinoma (ASCC), estimated to comprise greater than 70% of all anal cancer cases [5]. ASCC is known to have substantially increased in a number of countries over the last fifty years [6], [7], [8], [9], [10]. Few studies have simultaneously published incidence data on ASCC and anal adenocarcinoma (AAC). An Australian study of anal cancer for people diagnosed during the 1987–2005 period show increases over time in both ASCC and AAC age-standardised incidence rates per 100,000 person-years [6]. However, the investigators of this study did not estimate the magnitude of any future increase in incidence over time or investigate survival differences by histological subtype.
Compared to cancers of the colon and rectum [11], [12], little is understood about the survival outcomes of anal cancer in New South Wales and in other jurisdictions. This is primarily due to the fact that anal cancer is a rare outcome making trend measurement and multivariate analyses computationally difficult with sparse data. For example, the investigators of a study of relative survival for anorectal cancers in England and Wales combined data for cancers of the rectum and anus allowing for larger datasets to be analysed in a more complex manner [13]. There is the potential to mask important differences in survival outcomes when, in this example, data for two anatomical sites were aggregated. Given improvements in anal cancer treatment over the last 20 years [5], it is timely to measure incidence and survival for anal cancer in NSW including by histological subtype.
The aim of this study was to update incidence trends using more up-to-date cancer registration data, to predict the number of anal cancer cases in New South Wales (NSW) up to 2032, and to compare 5-year relative survival by histological subtype. We hypothesise that incidence for ASCC and AAC have increased over time. Similarly, 5-year survival has improved but that differences exist by sex and histological subtype.
Section snippets
Data sources
De-identified unit records for all unique cases of anal cancer diagnosed in NSW residents between 1972 and 2009 and notified to the NSW Cancer Registry were included. Operational details of the Registry have been published elsewhere [14]. Briefly, notifications to the Registry of invasive cancers are mandated under the NSW Public Health Act 2010.
The study cohort was defined using International Classification of Diseases for Oncology (ICD-O-3), 3rd edition, topography and morphology codes. All
Characteristics of persons with ASCC and AAC
Overall, there were 2724 newly diagnosed with anal cancer recorded in the NSW Cancer Registry between 1972 and 2009 (Table 2). The majority of these people (72%) were diagnosed with ASCC. There was an even distribution of the number of cases by age group for all anal cancers combined and for ASCC. People with AAC tended to be older at diagnosis, with 40% of these being diagnosed in people aged 75 years and older. More women than men were diagnosed with all anal cancers combined and ASCC, with
Discussion
Our study was based on high-quality anal cancer data over a 38-year period from the NSW Cancer Registry. We observed a significant, linear increase (AAPC of 1.6%) in incident cases of ASCC and a decline in the number of AAC cases. The incidence of ASCC is expected to steadily increase and make up the majority of cases of anal cancer in the future. We estimate there will be 198 cases of anal cancer in 2032. We also demonstrated a rise in 5-year relative survival for all histological subtypes and
Conflict of interest
None.
Authors’ contribution
J.Y., K.R., and M.S. designed the study. K.R. and M.S. analysed the data. M.S. wrote the manuscript. All authors revised the manuscript for intellectual content.
Sources of funding
This research was funded by a Cancer Epidemiology Linkage Grant from the Cancer Institute NSW. MS and JY were also supported by the Academic Leader, Cancer Epidemiology, grant awarded to The University of Sydney from the Cancer Institute NSW.
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