Progestin-only contraceptives have similar breast cancer risk

CANCER DIGEST – March 25, 2023 – The risk of breast cancer associated with progestin-only contraceptives is about the same as that of combined progestin-estrogen formulations, a new study shows.

Many women have chosen progesterone-only contraceptives based on studies showing a higher risk of breast cancer associated with combination contraceptives containing estrogen and progestin. Estrogen is a natural hormone and progestin is a synthetic version of the hormone progesterone.

It has long been known that combined estrogen and progesterone contraceptives have a slight increase in the risk of breast cancer ranging between 8 percent and 24 percent in different studies, and according to the UK’s Cancer Research, however, combination contraceptives are also linked to a slightly lower risk of cervical and ovarian cancers.

Less has been known about the breast cancer risk of progestin-only, or POP contraceptives. Using data from the UK’s Clinical Practice Research Datalink, researchers at Oxford University analyzed 9,498 women under age 50 who had invasive breast cancer diagnosed between 1996 and 2017, and compared them to 18,171 similar women without breast cancer. Their findings were published in the journal PLOS Medicine, March 21, 2023.

Overall, they found that 44 percent of the women with breast cancer and 39 percent of the non-cancer women had taken contraceptives for an average of 3 years before the breast cancer diagnosis or the equivalent period for the control group. About half of the prescriptions were for the POP formulation. In other words the odds of developing breast cancer among the POP women were slightly higher compared to the women without breast cancer.

The odds of breast cancer in the POP group, however worked out to be about the same as for women who took combination estrogen-progestin contraceptives, whether they took them orally, via injection or intra-uterine devices.

"When our findings for oral contraceptives are combined with results from previous studies (which included women in a wider age range), they suggest that the 15-year absolute excess risk of breast cancer associated with use of oral contraceptives ranges from 8 per 100,000 for users age 16 to 20 to about 265 per 100,000 for users from age 35 to 39," the researchers wrote.

Sources: ScienceDaily, March 23, 2023 and PLOS Medicine