Background
Oral contraceptives are known to influence the risk of cancers of the female reproductive system. Evidence regarding the relationship between injectable contraceptives and these cancers is limited, especially in black South Africans, among whom injectable contraceptives are used more commonly than oral contraceptives.Study Sample
The Johannesburg Cancer Case Control Study is a large ongoing case–control study recruiting self-defined black (not mixed race/ancestry) male and female cancer patients with all cancer types, conducted at the greater Johannesburg public referral hospitals that offer cancer treatment. Female patients recruited from 8 March 1995 to 31 December 2006 were included in the present analysis.
Table 1. Demographic and risk factor characteristics of case and control participants, according to use of hormonal contraceptives.
doi:10.1371/journal.pmed.1001182.t001
Table 2. Frequencies and adjusted odds ratios for breast, cervical, ovarian, and endometrial cancer according to ever/never oral and injectable contraceptive use combinations.
doi:10.1371/journal.pmed.1001182.t002
Figure 2. Odds ratio for ovarian and endometrial cancer in relation to use of hormonal contraceptives, according to duration of use.
Adjusted OR (95% CI) for (A) ovarian cancer and (B) endometrial cancer in relation to use of oral and injectable contraceptives, adjusted for age at diagnosis, year of diagnosis, education, tobacco smoking, alcohol consumption, parity/age at first birth, number of sexual partners, urban/rural residence, and province of birth. Squares represent ORs, and horizontal lines indicate 95% CI. Diamonds represent the ORs and confidence intervals for the group comprising women from all three exposure categories immediately above.
doi:10.1371/journal.pmed.1001182.g002
Conclusions
In this study, use of oral and of injectable hormonal contraceptives was associated with a transiently increased risk of breast and cervical cancer and, for long durations of use, with a reduced risk of ovarian and endometrial cancer. The observed effects of injectable and of oral contraceptives on cancer risk in this study did not appear to differ substantially.
