Preventive strategies for cervical and vaginal cancer – do they work?

Cervical cancer is the fourth most common cancer in women worldwide, and the third most common cause of death of cancer in women. In 2022, the incidence was estimated to 660 000 new cases and 350 000 deaths. In Sweden, around 450-550 new cases are diagnosed each year, and the incidence has been fairly stable since the 1980s.

In a new thesis from the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, PhD student and MD Hanna Milerad addresses clinical research questions on primary (HPV vaccination) and secondary (HPV-based cervical screening) prevention of cervical and vaginal cancer by targeting four groups of women in the organized cervical screening program. This includes women entering the screening program, women exiting the screening program, non-attenders in the screening program, and women previously treated for precancerous lesions. Each group of women fits under a certain level in the cervical cancer screening chain; 1) primary screening, 2) colposcopic examination, 3) treatment, 4) follow-up after treatment.

What are the most important results in your thesis?

“First, we studied women entering the screening program (age 23), where we compared HPV-vaccinated and unvaccinated women. Only 5% of vaccinated women had the most oncogenic types of HPV (HPV 16/18) compared to 33% of unvaccinated women. Colposcopy was a useful tool also in vaccinated women entering the screening program.

Second, we saw that 52% of women leaving the screening program (ages 56-64) and re- tested for HPV after 1 year were still HPV positive, and 40% after three years. HPV-HPV-testing may be used for the detection of precancerous lesions in women exiting the screening program, but puts more requirements on the colposcopist.

Third, women who hadn’t been screened in 10 years (ages 33-62) were sent HPV self-sampling kits. About 20% of them responded, and 15% of the kits were HPV positive. A high proportion of women had precancerous lesions or cervical cancer, showing that an opt-out strategy with HPV self-sampling and direct referral to colposcopy was feasible.

And finally, we studied women who had previously been treated for precancerous lesions. Between 1999-2018, 67,693 women were identified, and 213 developed cervical or vaginal cancer. Most noticeable was an elevated risk for invasive cancer during the first three years after treatment.

To summarize, primary prevention (HPV-vaccination) and secondary prevention (HPV-based screening) and a high quality throughout the whole cervical cancer screening chain are key measures to prevent cervical cancer. These strategies help catch the disease early and save lives.”

Why did you become interested in this topic?

“I am a gynecologist and I see women with precancerous lesions and cervical cancer daily in the hospital, which got me engaged in the topic. It is fascinating that this type of cancer can not only be prevented (by vaccination and screening), but also eliminated as a public health problem.”

What do you think should be done in future research?

“In my mind, two of the most important future challenges are:

  1. Reaching non-attenders in screening- and vaccination programs
  2. The medical assessment of women still at risk for cervical and vaginal cancer despite these preventative measures

To meet these future challenges more evidence is needed, but equally important is to take action, and I think that study designs that permit quality-control while implementing new strategies might be the way forward.”

Doctoral thesis

Evaluation of new and current preventive strategies for cervical and vaginal cancer.

Hanna Milerad. Karolinska Institutet (2024), ISBN: 978-91-8017-166-3.

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