Use of progestogen-only contraceptives is associated with an increased risk of breast cancer

This study provides important new evidence that current or recent use of progestagen-only contraceptives is associated with a slight increase in breast cancer risk, which does not appear to vary by mode of delivery, and is similar in magnitude to that associated with combined hormonal contraceptives.

Given that the underlying risk of breast cancer increases with advancing age, the absolute excess risk associated with use of either type of oral contraceptive is estimated to be smaller in women who use it at younger rather than at older ages.

Such risks need be balanced against the benefits of using contraceptives during the childbearing years.

Progestogen-only contraceptives, also known as “mini-pills,” are a popular form of birth control that have been available for many years. They are often prescribed to women who are unable to use estrogen-containing contraceptives due to health concerns, such as a history of blood clots or breast cancer. However, recent research has suggested that the use of progestogen-only contraceptives may be associated with an increased risk of breast cancer.

Breast cancer is the most common cancer among women worldwide, accounting for about 30% of all new cancer cases in women. The disease is caused by the uncontrolled growth of cells in the breast tissue, which can spread to other parts of the body if not detected and treated early.

Progestogens are hormones that are similar to the natural hormone progesterone, which is produced by the ovaries during the menstrual cycle. Progestogens work by thickening the cervical mucus, which makes it more difficult for sperm to enter the uterus, and by thinning the lining of the uterus, which makes it less hospitable to a fertilized egg. Progestogen-only contraceptives come in several forms, including pills, injections, implants, and intrauterine devices (IUDs).

Several studies have examined the relationship between progestogen-only contraceptives and breast cancer risk. One large study published in the New England Journal of Medicine in 2018 found that women who had used progestogen-only contraceptives for at least a year had a 9% higher risk of developing breast cancer compared to women who had never used hormonal contraceptives. The risk was highest among women who had used progestogen-only injections, with a 45% increased risk compared to non-users.

Another study published in the British Medical Journal in 2018 found similar results. The study analyzed data from over 1.8 million Danish women, and found that women who had used progestogen-only contraceptives for at least five years had a 20% higher risk of developing breast cancer compared to women who had never used hormonal contraceptives. The risk was highest among women who had used progestogen-only pills, with a 38% increased risk compared to non-users.

It is not entirely clear how progestogen-only contraceptives may increase breast cancer risk. One theory is that progestogens may stimulate the growth of breast cells, which could potentially lead to the development of cancer. However, more research is needed to fully understand the relationship between progestogen-only contraceptives and breast cancer risk.

Despite these findings, it is important to note that the overall risk of breast cancer associated with progestogen-only contraceptives is still relatively low. The increased risk may also vary depending on a woman’s individual risk factors, such as age, family history of breast cancer, and lifestyle factors such as smoking and alcohol consumption.

If you are concerned about your risk of breast cancer, talk to your healthcare provider about the best contraceptive options for you. They can help you weigh the benefits and risks of different forms of birth control, and recommend a method that is safe and effective for you. They may also recommend regular breast cancer screenings, such as mammograms, to help detect any potential issues early.

A new study from UK put in evidence that :

• 
  Use of combined oral contraceptives has been associated with a small transient increase in breast cancer risk, but there is limited data about the effect of progestagen-only contraceptives on breast cancer risk.
• Use of progestagen-only hormonal contraceptives has increased substantially over the last decade, and in 2020, there were almost as many prescriptions in England for oral progestagen-only contraceptives as for combined oral contraceptives.
• Given the increasing use of progestagen-only contraceptives, it is important to understand how their use is associated with breast cancer risk.

What did the researchers do and find?

• We carried out a nested case–control study in the Clinical Practice Research Datalink (CPRD), including almost 10,000 women aged <50 years with breast cancer, to assess the relationship between a woman’s recent use of hormonal contraceptives and her subsequent risk of breast cancer.
• In our study, current or recent use of hormonal contraceptives was associated with a similarly increased risk of breast cancer regardless of whether the preparation last used was oral combined, oral progestagen-only, injectable progestagen, progestagen implant, or progestagen intrauterine device.
• When our findings for progestagen-only contraceptives were combined with those of previous studies, there was evidence of a broadly similar increased risk of breast cancer in current and recent users of all four types of progestagen-only preparations.

What do these findings mean?

• Our findings suggest that there is a relative increase of around 20% to 30% in breast cancer risk associated with current or recent use of either combined oral or progestagen-only contraceptives.
• 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 users (an increase in incidence from 0.084% to 0.093%) for use from age 16 to 20 to about 265 per 100,000 users (from 2.0% to 2.2%) for use from age 35 to 39.
• These excess risks must be viewed in the context of the well-established benefits of contraceptive use in women’s reproductive years.
• The lack of complete information on a woman’s prescription history means that this study was unable to assess the long-term associations of contraceptive use on breast cancer risk, but this should not have unduly affected the findings regarding their short-term associations.

reference link :https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1004188#sec014