Cervical cancer is the fourth most common cancer in women, and 528,000 new cases were diagnosed worldwide in 2012. Pap smear is the major screening tool, but the screening interval varied by countries. Free-of- charge Pap has been provided to women aged 30 or over in Taiwan since 1995 annually, and recommendation was made for women to receive a Pap at least once within three years. The screening intervals should be evaluated according the evidence.
Women aged 30 or over and alive in Taiwan, in 2009 were enrolled. A total of 7,411,454 female residence without cervical cancer history were eligible. In 2010-2012, 5,141 invasive cervical cancer were diagnosed. The 3-year cervical cancer risk was calculated by stratification of women's Pap history from 1995 through 2009. According women received Pap or not in 2007, 2008 and 2009, they were classified into 8 groups. Among women received only one Pap in 2009, women were further defined into several sub-groups according the interval between their last Pap, such as 2-year (last Pap in 2007), 3-year (last Pap in 2006), et al. We aim to examine the cervical cancer risks across those groups with various screening intervals of 2-year, 3-year, 4-year or longer.
In 2007-2009, 3,731,557 women received 5,969,422 Paps. In the period, 567,635 women received annual Pap, their 3-year cervical cancer risk was 25.4. The risk for those women participated in screening in any two years was ranged from 27.2 to 32.0. Regarding women received only one Pap in 2007, 2008, 2009, the risk was 46.3, 34.4 and 42.3. The highest risk was 95.6, among those did not received any Pap in 2007-2009. The risk for the interval of last Pap in 2-, 3-, 4-, 5- and 6-year was 27.2, 32.0, 37.5, 49.5 and 61.5, respectively. Compare to the annual Pap group, the corresponding odds ratio was 1.13 (95%CI=0.88-1.45), 1.26 (95%CI=0.95-1.68), 1.47 (95%CI=1.06-2.05), 1.96 (95%CI=1.38-2.80) and 2.44 (95%CI=1.6-3.68), respectively.
Based on the evidence from our population study, cervical cancer risk increased while the intervals of two Pap increased. No significant risk was observed among annual screening, 2-year and 3-year of intervals. But a substantial increase of risk was detected when the interval was longer than 4 years. We recommend the interval between two Pap should be 2-3 years, but not longer than 4 years between two Paps