A nationwide cohort study has found contemporary forms of hormonal contraception prevented an estimated 21% of ovarian cancers in young women
About 100 million women around the world use hormonal contraception every day, but how does its use affect ovarian cancer risk?
Researchers from Scotland and Denmark followed a cohort of nearly 1.9 million Danish women aged 15-49 from 1995 to 2014.
They particularly wanted to look at the effect on newer hormonal contraceptives on women of reproductive age.
Most hormonal contraceptive use in the cohort (86%) related to combined oral products.
Other forms included in the study were progestogen-only oral contraceptives and the levonorgestrel releasing intrauterine device (IUD).
During 21.4 million person years, 1249 incidences of ovarian cancer occurred.
Among ever users of hormonal contraception (current or recent users, or former users), 478 ovarian cancers were recorded over 13.3 million person years, while never users had 771 ovarian cancers during 8.2 million person years.
Median age of ovarian cancer diagnosis was 44.4 years (IR 38.9-47.7).
Compared with never users, current or recent use of any hormonal contraception (≤ 1 year after stopping use) led to reduced risk of ovarian cancer (relative risk 0.58, 95% CI 0.49 to 0.68).
According to results published in the BMJ this week, former use (>1 year after stopping use) also led to a reduced risk (relative risk 0.77, 0.66 to 0.91).
Among ever users of hormonal contraception, the reduction in the age-standardised absolute rate of ovarian cancer was 3.2 per 100,000 person years.
Meanwhile the age-adjusted incidence of ovarian cancer was highest in women who were never users of contraception (7.5 per 100,000 person years).
Based on the results, the authors estimate use of hormonal contraception prevented 21% of ovarian cancers in the study population.
Reduced risk was stronger with increasing duration of hormonal contraceptive use, while reduced risk diminished over time since stopping use.
It became non-significant by 10 years after last use.
Current or recent users of progestogen-only products seemed to have a smaller reduction that users of combined oral contraceptives.
The authors point out that as the study was observational, no firm conclusions can be drawn about cause and effect.
However the results support the findings of studies of older products.
They also point out that they did not study older women, among whom most cases of ovarian cancer occur.
Therefore the results are only applicable to the group studied, i.e. women of reproductive age.
Researchers say that based on the results, it seems that “contemporary combined hormonal contraceptives are still associated with a reduced risk of ovarian cancer in women of reproductive age, with patterns similar to those seen with older combined oral products.
“The reduced risk seems to persist after stopping use, although it is not yet known how long for.
“Presently, there is insufficient evidence to suggest similar protection among exclusive users of progestogen-only products.”
Last year, the same cohort was studied for breast cancer risk by the same researchers, who found that hormonal contraceptives actually raised the risk of breast cancer.
As compared with women who had never used hormonal contraception, the relative risk of breast cancer among all current and recent users of hormonal contraception was 1.20 (95% CI, 1.14 to 1.26).
This risk increased from 1.09 (95% CI, 0.96 to 1.23) with less than one year of use to 1.38 (95% CI, 1.26 to 1.51) with more than 10 years of use (P=0.002), according to the paper published in the New England Journal of Medicine.
After discontinuation of hormonal contraception, the risk of breast cancer was still higher among the women who had used hormonal contraceptives for five years or more.
Women who currently or recently used the progestin-only intrauterine system also had a higher risk of breast cancer than women who had never used hormonal contraceptives (relative risk, 1.21; 95% CI, 1.11 to 1.33).
The overall absolute increase in breast cancers diagnosed among current and recent users of any hormonal contraceptive was 13 (95% CI, 10 to 16) per 100,000 person-years, or approximately one extra breast cancer for every 7690 women using hormonal contraception for one year.