Vulvar intraepithelial neoplasia: Incidence and long‐term risk of vulvar squamous cell carcinoma

The risk of vulvar squamous cell carcinoma (VSCC) in patients with high‐grade vulvar intraepithelial neoplasia (VIN) is considered lower in high‐grade squamous intraepithelial lesion (HSIL) compared to differentiated VIN (dVIN), but studies are limited. Our study investigated both the incidence of high‐grade VIN and the cumulative incidence of VSCC in patients with HSIL and dVIN separately. A database of women diagnosed with high‐grade VIN between 1991 and 2011 was constructed with data from the Dutch Pathology Registry (PALGA). The European standardized incidence rate (ESR) and VSCC risk were calculated, stratified for HSIL and dVIN. The effects of type of VIN (HSIL vs dVIN), age and lichen sclerosis (LS) were estimated by Cox regression. In total, 1148 patients were diagnosed with high‐grade VIN between 1991 and 2011. Between 1991‐1995 and 2006‐2011, the ESR of HSIL increased from 2.39 (per 100 000 woman‐years) to 3.26 and the ESR of dVIN increased from 0.02 to 0.08. The 10‐year cumulative VSCC risk was 10.3%; 9.7% for HSIL and 50.0% for dVIN (log rank P < .001). Type of VIN, age and presence of LS were independent risk factors for progression to VSCC, with hazard ratios of 3.0 (95% confidence interval [CI] 1.3‐7.1), 2.3 (95% CI 1.5‐3.4) and 3.1 (95% CI 1.8‐5.3), respectively. The incidence of high‐grade VIN is rising. Because of the high cancer risk in patients with dVIN, better identification and timely recognition are urgently needed.