Lifestyle and reproductive risk factors associated with anal cancer in women aged over 50 years

BACKGROUND: Anal cancer incidence increases with age and is higher in women than men. Risk factors in this group other than high-risk human papillomavirus infection are unclear. METHODS: In all, 1.3 million women were recruited in 1996–2001 and followed for incident anal cancer. Cox regression models were used to calculate relative risks (RRs) for anal cancer by various potential risk factors. RESULTS: Five hundred and seventeen incident anal cancers were registered over 13 years of follow-up. The largest RR was associated with a history of cervical intraepithelial neoplasia grade 3 (CIN 3; RR=4.03, 95% CI 2.59–6.28). Other factors associated with significantly increased risks in multivariate analyses were: ever smoking (RR=1.49, 1.24–1.80); previous use of oral contraceptives (RR=1.51, 1.24–1.83); nulliparity (RR=1.61, 1.24–2.07); tubal ligation (RR=1.39, 1.13–1.70) and not living with a partner (RR=1.82, 1.40–2.38). The association with smoking was significantly greater for squamous cell carcinoma than adenocarcinoma of the anus (RR 1.66 vs 0.89, P for heterogeneity=0.04). CONCLUSIONS: History of CIN 3, smoking, past oral contraceptive use, nulliparity, tubal ligation and not living with a partner are risk factors for anal cancer in women. There was a significant increase in risk associated with smoking for squamous cell anal cancers but not adenocarcinomas.