Progestogen-only contraceptive use is increasing, but information on the associated risks have been scarce. A large nested case-control study aimed to assess the breast cancer risk associated with the current or recent use of both combined and progestogen-only contraceptives in premenopausal women.
The study analysed data from a UK primary care database, the Clinical Practice Research Datalink (CPRD) on 9,498 women under the age of 50 with breast cancer whose prescribed oral combined contraceptives (containing oestrogen+progestogen), oral progestogen-only contraceptives, injectable progestogens, and progestogen-releasing IUD contraceptives were found to be at increased risk of breast cancer.
The data included 44% of women with breast cancer and 39% of women without breast cancer. All of them had a prescription for a hormonal contraceptive at an average of three years prior to diagnosis.
The data was used to calculate the strength of the association between each type of hormonal contraceptive used and the risk of breast cancer.
The ORs for each of these hormonal contraceptives were statistically significant, at around 1.2. to 1.3, regardless of whether the contraceptive use was a combined (estrogen and progestogen) oral preparation (OR=1.23 95%CI 1.14-1.32, p<0.001), a progestogen-only oral preparation (OR= 1.26 95% CI 1.16-1.37, p<0.001), an injected progestogen (OR= 1.25 95% CI 1.07-1.45, p=0.004), or a progestogen releasing intra-uterine device (OR=1.32 95% CI 1.17-1.49, p<0.001).
The average time between the last prescription and breast cancer diagnosis was around 3 years, which implies the results are linked to the current or recent use of hormonal preparations.
According to the ORs for breast cancer among users of each of these hormonal contraceptives, they were of similar magnitude to previous risks linked to the use of oral combined oestrogen-progestogen contraceptives. However, the findings for progestogen-only contraceptives when combined with previous findings, were clear in illustrating that there was an increased risk of breast cancer in current and recent users of all four types of progestogen-only preparations.
Overall, the findings suggest there is a relative increase of around 20% to 30% in breast cancer risk associated with the current or recent use of either combined oral or progestogen-only contraceptives.
However, the study does not include information on a woman’s prescription history, which means the authors were unable to interpret the long-term associations of contraceptive use on breast cancer risk.
Source: Plos Medicine
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