Combined Oral Contraceptives and Breast Cancer: an Unsolved Conundrum

Abstract

Purpose

This article’s purpose is to evaluate the quality of evidence and the magnitude of risk of breast cancer attributed to combined oral contraceptives (COCs). This is because whilst a number of studies have been done to assess this risk, evidence has been inconclusive and contradictory. This article is expected to aid clinicians when counselling women about COC and develop strategies to mitigate risk, if any, especially to women with pre-existing risk factors for breast cancer.

Materials and methods

Thirteen recent studies of diverse levels of evidence which attempt to assess the risk of breast cancer in COC users have been critically appraised. Six were systematic reviews/meta-analyses, and three were prospective cohort studies. Two case–control studies, a literature review and an observational study comprised the remaining four. Sample sizes of prospective cohort studies ranged from 46,022 to 1.8 million. Populations of various nationalities were included.

Results

There appears to be a marginal increase in risk of breast cancer with a relative risk ranging from 1.19 to 1.5. The risk increased with duration of use, particularly when exceeding 5 years. More recent studies have indicated higher risk when compared to studies before 1994.

Conclusion

The available evidence highlights the importance of adequate counselling when helping decide suitable contraceptive methods or hormonal therapy in general. It also suggests that short-term use may be safe in the absence of other risk factors for breast cancer. Caution needs to be exercised in women with pre-existing risk factors such as high BMI, smoking, family history of breast cancer or when there is a need to use it for longer than 5 years.