Australasian Science: Australia's authority on science since 1938

Injectable Contraceptives Match Pill for Cancer

By Stephen Luntz

Injectable contraceptives carry a similar risk and protective profile for reproductive cancers to their oral equivalents, a South African/Australian collaboration has found.

The use of oral contraceptives is believed to raise the risk of breast and cervical cancer while women are using it and for some time thereafter. On the other hand, the contraceptive pill offers long-lasting protection against ovarian and uterine cancer (AS, March 2012, p.45). The study of women in Soweto found similar effects applied to all four types of cancer among those using injectable contraceptives.

“Our study confirms previous findings that the use of oral hormonal contraceptives is associated with an increased risk of breast and cervical cancer,” says Prof Emily Banks of the Australian National University’s National Centre for Epidemiology and Population Health. This gave Banks confidence to use the same methodology to compare cancer rates in women who used hormonal contraceptives with those who did not.

“It’s tricky trying to measure four different diseases at once,” Banks notes. Having produced familiar results, Banks and Ms Margaret Urban of South Africa’s National Health Laboratory Service applied the same analysis to users of injectable contraceptives, which are popular among black South Africans. Their findings were published in PLoS Medicine.

Banks says that no significant difference was found in the rates of any of the four cancers among those who took contraceptives orally or by injection.

She notes that for women in the developed world, the pill’s “net effect is cancer-protective”. The same presumably applies for women who use injectable contraceptives.

But in the developing world, where the lack of access to pap smears has produced much higher cervical cancer rates, the comparison is not as straightforward. “However, in countries with weaker health systems, pregnancy itself is a health risk, and it is important to remember that these are highly effective contraceptives,” Banks says.