The association between body mass index and vulvar and vaginal cancer incidence: findings from a large Norwegian cohort study.

Background: There is limited evidence of potential associations between body mass index (BMI) and risk of vulvar and vaginal cancer. We explored these associations in a large cohort of Norwegian women.

Methods: The analytical dataset included 889,441 women aged 16-75 years at baseline in 1963-1975. Multivariable Cox regression analyses were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations between BMI and vulvar and vaginal cancer incidence.

Results: During 30.1 million person-years of follow-up, 1748 incident vulvar and 408 incident vaginal cancer cases occurred. The HRs (95% CIs) for vulvar cancer for a BMI of 15- < 18.5, 18.5- < 25, 25- < 30, 30- < 35, ≥ 35 were 0.62 (0.38-1.01), 1.00 (reference), 1.23 (1.10-1.40), 1.43 (1.23-1.66) and 1.72 (1.35-2.20, p_trend < 0.001), and per 5 kg/m² increment was 1.20 (1.13-1.26). The corresponding HRs (95% CIs) for vaginal cancer were 1.05 (0.52-2.15), 1.00, 0.89 (0.71-1.12), 0.95 (0.68-1.34), and 2.01 (1.29-3.13, p_trend < 0.001), respectively, and per 5 kg/m² was 1.11 (0.99-1.25). The HR (95% CI) per 5 kg/m² increase in BMI at ages 16-29 was 1.28 (1.07-1.54, n = 250 cases) for vulvar and 1.53 (1.11-2.11, n = 66 cases) for vaginal cancers. The HR (95% CI) per 5 kg/m² for early-onset (< 50 years age at diagnosis) vulvar cancer was 0.92 (0.66-1.28, n = 87 cases) and 1.70 (1.05-2.76, n = 21 cases) for vaginal cancer.

Conclusion: These results further support the associations between higher BMI and increased risk of vulvar and vaginal cancers, with suggestive stronger associations between BMI in early adulthood for both cancers and for early-onset vaginal cancer. Further studies are needed to elucidate these findings and investigate the underlying mechanisms.