A study of 1.8 million women demonstrated an increased risk of breast cancer with hormonal contraceptive use — including combined oral contraception (COC), progestin-only pills (POPs), and intrauterine systems — with a dose-response relationship.1

“Breast cancer is the most frequent cancer in women (12% lifetime risk) and hormonal contraception the most frequent medical exposure in women (40% of all women of reproductive age in Denmark). Any relationship will have a major health impact,” Øjvind Lidegaard, MD, DMSc, of the University of Copenhagen in Denmark, told Cancer Therapy Advisor.

The risk for breast cancer with hormonal contraceptive use is not a new concept — the prescribing information for oral contraceptives, for example, cautions that there is a potential for breast cancer development. Findings from epidemiologic studies have, however, been mixed, with only some data sets showing an association between hormonal contraceptive use and oncogenesis.

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The mechanism likely underlying the association between breast cancer and hormonal contraception is that “exogenous hormones are expected to influence breast tissue as do the natural sex hormones, estrogen and progestin,” Dr Lidegaard said.

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Estrogen and progesterone are known drivers of hormone receptor (HR)-positive breast cancer, the predominant subtype of breast cancer.2 Moreover, known risk factors for the development of HR-positive breast cancer include events that determine estrogen and progesterone exposure, including age of menarche, age of menopause, pregnancy, and exogenous hormone exposures. Drugs that impair estrogen receptor signaling, such as tamoxifen or aromatase inhibitors, also reduce the risk of breast cancer among women at high risk.