Elsevier

Cancer Epidemiology

Volume 39, Issue 6, December 2015, Pages 842-847
Cancer Epidemiology

Trends in incidence and survival for anal cancer in New South Wales, Australia, 1972–2009

https://doi.org/10.1016/j.canep.2015.10.008Get rights and content

Highlights

  • A steady, linear increase in the incidence of anal squamous cell carcinomas (ASCC) has occurred over time.

  • Incidence of anal adenocarcinoma has declined in the last 10 years.

  • Survival for anal cancer varies substantially by gender and histological subtype.

  • The majority of future anal cancer cases are likely to be ASCC.

Abstract

Introduction

Little is known about the incidence and survival of anal cancer in New South Wales (NSW), Australia, as anal cancer cases are often grouped together with other colorectal cancers in descriptive epidemiological analyses.

Methods

We studied patterns and trends in the incidence and survival of people diagnosed with anal cancer in NSW, Australia, 1972–2009 (n = 2724). We also predicted anal cancer incidence in NSW during 2010–2032. Given the human papilloma virus-associated aetiology for most anal cancers, we quantified these changes over time in incidence and survival by histological subtype: anal squamous cell carcinoma (ASCC); and anal adenocarcinoma (AAC).

Results

There was a linear increase in incident anal cancer cases in NSW with an average annual percentage change (AAPC) of 1.6 (95% CI 1.1–2.0) such that, in combination with age-period-cohort modelling, we predict there will be 198 cases of anal cancer in the 2032 calendar year (95% CI 169–236). Almost all of these anal cancer cases are projected to be ASCC (94%). Survival improved over time regardless of histological subtype. However, five-year relative survival was substantially higher for people with ASCC (70% (95% CI 66–74%)) compared to AAC (51% (95% CI 43–59%)), a 37% difference. Survival was also greater for women (69% (95% CI 64–73%)) with ASCC compared to men (55% (95% CI 50–60%)). It was not possible to estimate survival by stage at diagnosis particularly given that 8% of all cases were recorded as having distant stage and 22% had missing stage data.

Interpretation

Aetiological explanations, namely exposure to oncogenic types of human papillomavirus, along with demographic changes most likely explain the actual and projected increase in ASCC case numbers. Survival differences by gender and histological subtype point to areas where further research is warranted to improve treatment and outcomes for all anal cancer patients.

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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