Worldwide trends in cervical cancer incidence: Impact of screening against changes in disease risk factors
Introduction
Invasive cervical cancer (ICC) is the third most common cancer in women worldwide, with an estimated 529,000 new cases in 2008. The burden of cervical cancer varies considerably worldwide, with more than 85% of the global burden occurring in low-to-medium-resource countries, where it is still in many instances the most common malignancy in women.1 Incidence and mortality rates of ICC have fallen over the past decades in a number of countries, mainly in high-resource countries following the introduction of screening programmes for cervical cancer.2, 3, 4, 5 However, stable or even rising trends have been observed in countries where screening activity is either lacking or suffers from low-quality and low-coverage.2, 4, 6
Persistent infection with oncogenic human papillomavirus (HPV) is considered a necessary cause of ICC.7 Other cofactors, such as high number of sexual partners, young age at first sexual intercourse,8 multiparity,9 oral contraceptive use,10 smoking11 and HIV infection,7 influence either the risk of acquisition of HPV infection or the progression to ICC. HPV infection could not be accurately detected in large epidemiological studies until the 1980s, and little is known on time trends of HPV prevalence in different populations.12, 13
The comparison of ICC trends in different countries offers, therefore, an opportunity to assess the impact of screening efforts set against background changes in ICC risk factors.2 For this purpose, we performed age-period-cohort (APC) analyses using incidence data from high-quality and longstanding population-based cancer registries from 38 countries to examine ICC patterns and trends across the major world regions.
Section snippets
Incidence data
New cases of ICC by age and calendar year of diagnosis were obtained from population-based cancer registries from the series Cancer Incidence in Five Continents (CI5) Volumes I to IX.14 Population data were obtained from the same sources. Registries were included in our study if there was availability of at least 15 consecutive years of data and they were included in the last volume of CI5. The last year of diagnosis available in Volume IX of CI5 was 2002, but more recent data accessible
ASRs of incident cervical cancer
Table 1 shows the incidence series available, by country, and the number of incident ICC cases, person-years and truncated ASRs for the period 1998–2002 and ages 30–74. Incidence rates varied approximately 10-fold across study populations, with the lowest ASR in 1998–2002 observed in Finland (ASR = 8 per 100,000) and the highest in Uganda (ASR = 104). Incidence rates in North America, Australia and Europe ranged between eight in Finland and 21 in Denmark and Norway. In Eastern Europe, ASRs were
Discussion
This descriptive analysis suggests that, despite general declines in ASRs globally, the risk of cervical cancer by calendar period of diagnosis and birth cohort varied substantially by country and world region in the last decades. Strong downward trends in ICC risk by period were observed in the highest-income countries in contrast to the mainly stable period curves seen elsewhere. Successive cohorts of women born in 1940–50 and thereafter exhibited either increases in ICC risk (e.g. in nearly
Contributors
S.V. and F.B. conceived and designed the study. J.L.T. provided cancer incidence estimates adapted from the Cancer Incidence in Five Continents database. S.V., M.P. and J.L.T. contributed to data collection and data analysis. S.V., F.B. and S.F. wrote the draft manuscript. All authors contributed to the interpretation of the data and approved the final manuscript.
Role of the funding source
The funders had no role in the design of the study; the collection, analysis and interpretation of the data; the decision to submit for publication; or the writing of the manuscript. The views expressed in this publication are those of the authors and not necessarily those of the funders.
Conflict of interest statement
None declared.
Acknowledgements
This work was supported by a grant from the Bill and Melinda Gates Foundation (BMGF), USA, (Grant Number OPP1053353).
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