By: Diane M. Harper, et al.
We read with interest the conclusion that Chris Bauch and colleagues1 presented, indicating that the incidence of cervical cancer would be very unlikely to increase as a result of human papillomavirus (HPV) vaccination. The investigators conclude that screening coverage in a population is unlikely to decline to levels that would be necessary to lead to an increase cervical cancer incidence—this being an 80% decrease in screening with 30% vaccine coverage. We refute their conclusions and present data from the UK and Finland that show that screening less than 20% of young women resulted in a substantial increase in cervical cancer incidence in an unvaccinated female population. With increasing background exposure to high-risk HPV, the incidence of cervical cancer did not decrease in the UK until at least 70% of the population were appropriately screened.2, 3 Likewise, when less than 70% of the population is screened, only individual benefits result and the population incidence of cervical cancer is not reduced.
Finland adopted organised cervical cancer screening in the early 1960s. For the first decade of organised screening, incidence was 14–16 per 100 000 woman-years,4 effectively finding the prevalent cancer cases in the previously unscreened population. By 1970, organised screening coverage had reached at least 70% of the target population, and the incidence of invasive cervical cancer dropped sharply by 75% over the next 20 years. Incidence rose again to an overall level of 4 per 100 000 woman-years over the next 10 years.5 Why did this happen?
In 1985, when cervical cancer incidence was still quickly declining, the actual incidence corresponded to predictions that were based on previous decreases;6 however, for every subsequent year, the rate of cervical cancer was higher than predicted for women aged 30–39 years4, 5—the peak age group for cervical cancer. In Finland, every year the rate continued to increase by 3 per 100 000 woman-years until it was more than four times higher than the expected rate per 1 million person-years for 30–39 year old women (figure 1); a real step backwards for cervical cancer prevention in the population. In contrast, over the same period, cancer rates for women over 50 years old continued to decrease as expected because over 70% of these women still actively attended screening. Reasons for increases in cervical cancer in younger women were a willful lack of screening and rapid increases in HPV16 incidence and prevalence.7 The Finnish Mass Screening Registry5 reported that less than 60% of women less than 40 years of age accepted the invitation to be screened in 2003, and only 20% of the women 25–30 years of age participated in the screening programme (figure 2). Assuming low vaccine coverage (30%), which gains no herd benefit,8 these data fulfil the thresholds that Bauch and colleagues1 defined for cervical cancers to increase after HPV vaccination. Willful lack of screening participation is already occurring in our youngest women, who have the lowest awareness of the magnitude of the morbidity and mortality of cervical cancer. An increase in cervical cancer can be seen as soon as 5 years after a willful decrease of participation in screening programmes and an ongoing high-risk HPV epidemic.
Organised HPV vaccination combined with screening could potentially prevent most cervical cancer.
Read the full article: http://www.thelancet.com/journals/laninf/article/PIIS1473-3099(10)70182-1/fulltext