Table 1.
Summary of of IARC evidence for combined oral contraceptive use and risk of cancer and relative risk estimates and sources
| IARC Conclusions | Relative Risk Source and Estimates | ||||
|---|---|---|---|---|---|
| Cancer Site (ICD-10 codes) | Level of evidence | Relation between risk and usage patterns | Reference | Study type | Relative Risk |
| Liver (C22) | Sufficient | Risk occurs in populations at low risk of Hepatitis B (HBV) infection (in HBV endemic populations, risk is assumed to be masked by the large risk associated with HBV infection) | N/Aa | ||
| Breast (C50) | Sufficient | Risk occurs in young women, among current and recent users only | Collaborative Group on Hormonal Factors in Breast Cancer4 | Pooled individual data from 54 studies (10 cohort, 44 case-control) conducted in 25 countries. 53,297 women with breast cancer and 100,239 women without breast cancer were included. | Current versus never use: RR = 1.24 (95%CI 1.15–1.33) |
| Uterine Cervix (C53) | Sufficient | Risk increases with duration of use and declines after cessation of use | International Collaboration of Epidemiological Studies of Cervical Cancer5 | Reanalysis of individual participant data from 24 studies (9 cohort and 15 case-control) from 26 countries worldwide (about half from less developed countries). 16,573 women with cervical cancer and 35,509 women without cervical cancer were included. | Current versus never use: RR = 1.65 (FSEb 0.08) |
| Endometrium (C54, C55) | Sufficient evidence that cancer risk is reduced | Reduction in risk increases with duration of use and lasts for at least two decades after cessation of use | Dossus et al7 | EPIC Cohort Study (multicentre prospective cohort study in 10 European countries). Approximately 370,000 female participants. 1,017 endometrial cancer cases diagnosed during an average of 8.7 years of follow-up. | Duration of use (amongst ever users): RR = 0.92 (95%CI 0.90–0.94) per year of use |
| Ovary (C56) | Sufficient evidence that cancer risk Is reduced | Reduction of risk increases with duration of use and lasts for at least three decades after cessation of use | Collaborative Group on Epidemiological Studies of Ovarian Cancer6 | Pooled individual data for 23257 women with ovarian cancer, and 87303 women without ovarian cancer from 45 studies (13 cohort, 19 case-control with population controls, and 13 case-control with hospital controls) in 21 countries. | Duration of use (amongst ever users); RR = 0.80 (95%CI 0.77–0.82) per 5 years of use |
Source: IARC Working Group on the Evaluation of Carcinogenic Risks to Humans1
a: PAFs not calculated for liver cancer; b: FSE= floating standard error