Abstract
The aim of this study was to assess trends in the age-specific incidence of vulvar cancer in 13 high-income countries satisfying a priori conditions regarding the availability of cancer registry data over a 20-year period; these were Canada, the United States, nine European countries, Australia and Japan. Five-yearly incidence and population at risk were obtained from the International Agency for Research on Cancer's Cancer Incidence in Five Continents for the years 1988-1992 (Volume 7) to 2003-2007 (Volume 10). The 5-yearly average percent change (AvPC) over the period and standardised rate ratios (SRRs) for 2003-2007 versus 1988-1992 were used to assess changes in the age-standardised incidence rates of vulvar cancer for all ages, and for <60 years and 601 years. During the study period, the 5-yearly AvPC across the 13 countries increased by 4.6% (p=0.005) in women of all ages, and 11.6% (p=0.02) in those <60 years. No change was observed in women aged 601 years (5-yearly AvPC=0.1%, p=0.94). The SRR for 2003-2007 versus 1988-1992 was significantly elevated in women <60 years of age (SRR=1.38, 95% CI: 1.30-1.46), but not in women of 601 years (SRR=1.01, 95% CI: 0.97-1.05). The increase in incidence in women <60 years of age drove a significant increase in the overall SRR in women of all ages (SRR=1.14, 95% CI: 1.11-1.18). Some differences in the specific findings at the individual country level were observed. The findings are consistent with changing sexual behaviours and increasing levels of exposure to human papillomavirus (HPV) in cohorts born around/after about 1950, but younger cohorts offered HPV vaccination are likely to receive some protection against developing vulvar cancer in the future.