Table 2.

Summary of combined oral contraceptive (COC) use and risk of cancer.

Studied relation	Reference	Type	Level of evidence	Material	Main findings	Relative risk (95% confidence interval)
Use of COC in relation to risk of epithelial ovarian cancer	Beral et al. [2008]	Meta-analysis	2	23,257 cases 87,303 controls	• Decreased risk in COC ever users	0.73 (0.70–0.76)
					• A more pronounced effect by duration of use
	Havrilesky et al. [2013]	Systematic review/meta-analysis		657,055 women, 3,981,072 women years	• The protective effect lasts at least 30 years after use	0.73 (0.66–0.81)
	Hannaford et al. [2007]	Prospective cohort	2	46,000 women 744,000 women years	• Decreased risk in COC ever-users	0.54 (0.40–0.71)
					• A more pronounced effect by duration of use
	Vessey and Painter [2006]	Prospective cohort		17,032 women, 540,000 women years	• The protective effect lasts at least 15–20 years	0.5 (0.3–0.7)
Use of COC in relation to endometrial cancer risk	Gierisch et al. [2013]	Systematic review/meta-analysis	2	308,198 women	• Risk reduction among COC ever-users	0.57 (0.43–0.77)
					• The effect lasts at least 20 years
Use of COC in relation to colorectal cancer risk	Gierisch et al. [2013]	Systematic review/meta-analysis	2	2,969,189 women years	• Risk reduction in COC ever-users	0.86 (0.79–0.95)
					• Big variation between studies
					• No established relation between duration of use and effect
Use of COC in relation to breast cancer risk	Gierisch et al. [2013]	Systematic review/meta-analysis	2	317,341 women	• Small increase in risk during current use	1.08 (1.00–1.17)
					• The increased risk declines and disappears 10 years after cessation
	Collaborative Group on Hormonal Factors in Breast Cancer [1996]	Systematic review/meta-analysis	2	53,297 cases 100,239 controls	• The increased risk is highest among young users	1.24 (1.15–1.33)
Use of COC in relation to cervical cancer risk	Appleby et al. [2007]	Systematic review/meta-analysis	2	16,573 cases 35,509 controls	• Increased risk in current users	≥5 year 1.9 (1.69–2.13)
					• The increased risk declines and disappears 10 years after cessation
	Longatto-Filho et al. [2011]	Prospective cohort	2	12,114 women	• Presence of Hr-HPV was related to risk	No independent increased risk in COC usersNo trend if used <5 years; use 5–9 years: 2.82 (1.46–5.42); use >10 years 4.03(2.09–8.02)
	Gierisch et al. [2013]	Systematic review/heterogeneity made meta-analysis impossible; pooled data from study of good quality	2	1561 cases 1916 controls	• Increased risk only in Hr-HPV positive women

Hr-HPV, high-risk human papillomavirus