An extensive study has found oral contraceptive use is associated with reduction in some cancers for up to 35 years
The study of more than 46,000 women recruited by the UK Royal College of General Practitioners in 1968 and 1969 observed participants for up to 44 years, equalling nearly 1.3 million women-years of observation.
Rates of different cancers were calculated for “ever” and “never” users of combined oral contraceptives and analysis of any cancer risk included only the first cancer for each type.
Most OCPs used in the study contained 50 µg of estrogen combined with progestogen.
Ever use of OCPs was found to be associated with reduced risk of:
- Colorectal cancer (incidence rate ratio 0.81; 99% CI, 0.66-0.99);
- Endometrial cancer (incidence rate ratio 0.66, 99% CI, 0.48-0.89);
- Ovarian cancer (incidence rate ratio 0.67, 99% CI, 0.50-0.89);
- Lymphatic and hematopoietic cancer (incidence rate ratio 0.74, 99% CI, 0.58-0.94).
Endometrial, ovarian, and colorectal cancer benefits were found to persist for at least 30 years among past users of OCPs.
The study results correlate with other global evidence that OCPs provides prolonged protection.
“Our results suggest that users of oral contraceptives are protected from colorectal, endometrial, and ovarian cancer for many years after stopping, perhaps for >35 years for colorectal and ovarian cancer,” say the authors from the University of Aberdeen in the UK.
“There was no evidence of new cancer risks appearing later in life among women who had used oral contraceptives.
“These results provide strong evidence that most women do not expose themselves to long-term cancer harm if they choose to use oral contraception; indeed, many are likely to be protected.”
An increased risk of lung cancer was seen only among ever users who smoked at recruitment.
Meanwhile, an increase risk of breast and cervical cancer was seen in current and recent users, although the risk appeared to be lost within 5-10 years of stopping OCP use.
Widespread implementation of effective cervical cancer prevention measures such as HPV vaccination or cervical cancer screening should result in reduced cervical cancer incidence over time and result in an even more favourable overall balance in OCP users, the authors add.
“It is reassuring to find that, in one of the regions of the world with high cancer incidence among women, there is no indication of substantial lifetime cancer risk among ever users >35 years after stopping this population method of contraception,” they conclude.
American Journal of Obstetrics & Gynaecology 2017; online 8 February 2017