Incidence of vulvar high-grade precancerous lesions and cancer in Denmark before and after introduction of HPV vaccination

Abstract

Objective: To assess the incidence of vulvar high-grade precancerous lesions and cancer in Denmark during 1997-2018.

Methods: We identified incident vulvar cancer cases in the Danish Cancer Registry and incident cases of vulvar precancerous lesions in the Danish Pathology Register. We calculated age-standardized incidence rates of vulvar squamous cell carcinoma (VSCC), non-SCC and precancerous lesions, and age-specific incidence rates of VSCC and precancerous lesions. Incidence trends were evaluated using linear Poisson regression to estimate the average annual percentage change (AAPC). For vulvar precancerous lesions, trends were evaluated in the period before (1997-2007) and after (2008-2018) implementation of HPV vaccination.

Results: In the 22-year study period, the age-standardized incidence rate of VSCC increased from 1.23 (1997-1998) to 1.98 per 100,000 (2017-2018), corresponding to an average yearly increase of 2.95% (95%CI: 2.15-3.75). The incidence of non-SCC increased only slightly. Overall, the incidence of vulvar precancerous lesions increased (AAPC = 2.38%; 95%CI: 1.75-3.02). After implementation of HPV vaccination, the incidence of vulvar precancerous lesions decreased significantly in women aged <20 (AAPC = -22.10% (95%CI: -35.27 to -6.26)) and 20-29 years (AAPC = -6.57, 95% CI: -10.63 to -2.33), whereas the incidence increased in the majority of age groups ≥50 years.

Conclusions: Overall, the incidence of VSCC and vulvar precancerous lesions increased during 1997-2018. However, after introduction of HPV vaccination, the incidence of vulvar precancerous lesions decreased among women aged <20 and 20-29 years, pointing towards a possible effect of HPV vaccination in this group. This development should be followed in the future.

Keywords: Human papillomavirus; Incidence; Squamous cell carcinoma; Vulvar cancer; Vulvar high-grade squamous intraepithelial lesion.