ORIGINAL PAPER A case–control study of the protective benefit of cervical screening against invasive cervical cancer in NSW women Baohui Yang Æ Stephen Morrell Æ Yeqin Zuo Æ David Roder Æ Elizabeth Tracey Æ Paul Jelfs Received: 10 July 2007 / Accepted: 10 January 2008 / Published online: 20 February 2008 Ó Springer Science+Business Media B.V. 2008 Abstract Objective To examine the effects of different Pap screening patterns in preventing invasive cervical cancer among women in New South Wales, Australia. Methods A total of 877 women aged 20–69 years diag- nosed with invasive cervical cancer during 2000–2003 were matched with 2,614 controls by month and year of birth. Screening behavior patterns in 4 years preceding the time of cancer diagnosis in the cases were classified into none (no Pap test in the 4 years), ‘irregular’ (1 of the 4 years with Pap test(s)), and ‘regular’ (2 or more of the 4 years with a Pap test), and compared with those in the matched non-cases over the same period. Conditional logistic regression modeling was used to estimate the rel- ative risk, approximated by the odds ratio, of invasive cervical cancer for regular and irregular cervical screening compared with no screening in the previous 4 years, before and after controlling for potential confounders including the first recorded Pap test result in the preceding 6-year reference period. Results Compared with no screening, irregular Pap screening in the 4 years preceding the cancer diagnosis is estimated to reduce the risk of invasive cervical cancer by about 85% (RR = 0.15, 95% CI: 0.120–0.19); regular Pap screening reduces the risk by about 96% (RR = 0.04, 95% CI: 0.03–0.05). After adjusting for the index Pap test result, the relative risks for invasive cervical cancer were 0.19 (95% CI: 0.13–0.27) for irregular screening and 0.07 (95% CI: 0.04–0.10) for regular Pap screening. Conclusions Regular and irregular Pap tests among women aged 20–69 years were highly effective in prevent- ing invasive cancer. At-risk women with no Pap test history should be encouraged to undergo a Pap test every 2 years, but any Pap screening over a 4-year period remains highly pro- tective against future invasive cervical cancer. Keywords Cervical screening  Cervical cancer  Case–control study Introduction The Papanicolaou smear is an effective health screen for women because it not only can detect cervical cancer at a presymptomatic stage, but can also pick up precancerous lesions of the uterine cervix. The early treatment of a presymptomatic invasive cervical cancer and preventive B. Yang (&)  S. Morrell  Y. Zuo  E. Tracey NSW Department of Health, Health Survey program, Cancer Institute New South Wales, Level 3 73 Miller Street, Sydney, NSW 2059, Australia e-mail: byang@doh.health.nsw.gov.au Y. Zuo e-mail: yeqin.zuo@cancerinstitute.org.au E. Tracey e-mail: Elizabeth.tracey@cancerinstitute.org.au S. Morrell School of Public Health, University of Sydney, Sydney, NSW, Australia e-mail: Stephen.morrell@cancerinstitute.org.au D. Roder Cancer Council of South Australia, Sydney, NSW, Australia e-mail: droder@cancersa.org.au P. Jelfs Clinical Oncological Society of Australia, Sydney, NSW, Australia e-mail: pauljelfs@grapevine.com.au 123 Cancer Causes Control (2008) 19:569–576 DOI 10.1007/s10552-008-9118-9