Association of levonorgestrel-containing emergency contraceptive pills with breast cancer in premenopausal Latin American women: the PRECAMA study.

[BACKGROUND] The emergency contraceptive pill (ECP) contains progestin, which can have proliferative effects when used intermittently and thus increase the risk of breast cancer.

[METHODS] We investigated the association between the use of ECP and breast cancer risk in premenopausal Latin American women from 2012 to 2023. We hypothesized that ECP use increases breast cancer risk. We used data from a case-control study (the PRECAMA study) conducted among premenopausal Latin American women. We evaluated variables such as having ever used an ECP, sociodemographic factors, anthropometric and lifestyle characteristics, and gynecologic-obstetric history. We estimated adjusted odds ratios (ORs) via conditional logistic regression models.

[RESULTS] We analyzed data from 466 cases and 466 controls from Colombia, and Mexico. The prevalence of ever use of the ECP was 26.8% in cases and 15.0% in controls. Women who had ever used the ECP had an increased risk of breast cancer than those who never used ECP, after adjusting for potential confounders (OR = 1.71 95% confidence interval (CI), 1.16-2.53). When compared to Never users, those who reported using ECP 1-2 times, or ≥3 times, increased their risk (OR = 1.52, 95% CI 0.95-2.45; OR = 2.03, 95% CI 1.15-3.58, respectively).

[CONCLUSIONS] ECP use was associated with higher odds of breast cancer in premenopausal women; however, because ECP use co-occurred with other hormonal contraceptive use, the association cannot be attributed to ECPs in isolation.

[IMPACT] We recommend replicating these findings across diverse populations and using longitudinal study designs to strengthen the validity of these results.