Breast Cancer and the Mini Pill: All You Need to Know

A recent study (1) has found there to be an increased link between breast cancer and the Progesterone only Pill (POP) or Mini Pill. Past studies had looked at the association between the Combined Oral Contraceptive Pill (COCP) and breast cancer, but this is the first of its kind to examine the POP. Any link between the POP and breast cancer previously surmised was by extrapolation from studies of the COCP. With POP usage increasing in recent years, it was time to clarify the risks with a study devoted to just that. 

How Was the Study Carried out?

The study looked at almost 10,000 women diagnosed with breast cancer over a 7-year period and compared them with just over 18,000 ‘matched controls.’ Essentially these were women who did not have breast cancer and were matched for variables such as age, GP practice, body mass index, number of recorded births, time since last birth, and alcohol intake. Their contraceptive history was then examined. 

What Did the Results show?

Overall, 44% of the cases and 39% of control women had a prescription for a hormonal contraceptive an average of 3 years before diagnosis, around half of whom had last been prescribed a progestogen-only contraceptive. The risks were similarly raised if the last hormonal contraceptive prescription was for a COCP, POP, injected progesterone, or progesterone-releasing intrauterine devices (IUD such as the Mirena coil.) 

What does this mean? 

The findings suggest that 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 progesterone-only contraceptives. The risk is similar for both contraceptives. 

So, should I not take the mini pill based on these findings?

Obviously, the risks need to be considered when taking any medication. However, to understand the risks properly it helps to understand the relative risk and absolute risks. The relative risk of taking hormonal contraception is an increased breast cancer risk of 20-30%, however, this is in addition to the background risk.

Every woman has a background risk of breast cancer which is based on a number of risk factors such as age, BMI, alcohol intake, family history, age at which periods start, age of menopause, and activity levels. Someone with a normal BMI, with no significant family history who doesn’t drink alcohol and who exercises more than 2.5 hours per week for example would have a low background risk of breast cancer, and a 20-30% risk increase would not increase their absolute risk by a lot. 

What is the Absolute Risk Associated with Hormonal Contraception? 

The team that performed this study also combined their results with those of 12 previous observational studies which took into account a larger age range of women to calculate the absolute risk. The results showed that hormonal contraception would result in an extra 8 breast cancer cases per 100,000 users between the ages of 16-20 years and an extra 265 breast cancer risk between the ages of 35-39. This amounts to an increase in breast cancer risk for the 15 years after stopping hormonal contraception from 0.5 % to 0.57% in women who use it between the ages of 25-29. In women who take it between the ages of 35-39, the risk rises from 2.0 to 2.2 %. 

So, as you can see the absolute risk is actually quite small. 

It’s also important to remember that the increased risk does decline over time. An increased relative risk of 33 % drops to around 15% after 5 years of stopping oral contraception.

Are there any advantages to the Progesterone only Pill?

Yes, there are lots including: 

1. Periods usually become lighter and, in many cases, may stop altogether. The POP can cause some irregular bleeding on initiation, but after this most women find their periods are light, or often non-existent. For this reason, the POP can be used to treat heavy periods, particularly in conditions such as Endometriosis where its desirable to suppress menstruation, as well as provide contraception. 
    
2. The Progestogen-only pill has been shown not to affect glucose tolerance or other hormones such as Thyroid function. It does not affect liver function, blood clotting or platelet function hence does not increase the risk of blood clots the same way the COCP does. For this reason, it can be prescribed in situations where the combined pill cannot for example in women above 35 years who smoke, in women with migraine with aura, or who have had a past history of blood clots. (2)
    
3. It can be prescribed up until the age of 55 years, therefore it can be used alongside Hormone Replacement Therapy (HRT) as a form of contraception. 
    
4. It is likely to confer some protection against endometrial cancer. A Cochrane review has shown that the use of oestrogen alone in the context of HRT causes the thickening of the womb lining and that use of progestogen causes a reduction in this thickness (3). We know that the use of the COCP reduces the risk of endometrial cancer and the longer you use it the greater the degree of protection. (4) It is likely that this is due to the progestogenic component, however studies devoted to looking at the effects of the mini pill on endometrial cancer risk to date have been very small, and further studies are needed. 

If you need further advice, speak to one of our pharmacists today. 

References

1. Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case–control study and meta-analysis Danielle Fitzpatrick,Kirstin Pirie ,Gillian Reeves,Jane Green,
   Valerie Beral † Published: March 21, 2023
2. The progestogen-only mini-pill. Contraception . 1982 Oct;26(4):373-88. doi: 10.1016/0010-7824(82)90104-4. S Graham, I S Fraser
3. Furness S, Roberts H, Marjoribanks J, Lethaby A. Hormone therapy in postmenopausal women andrisk of endometrial hyperplasia. Cochrane Database of Systematic Reviews 2012, Issue 8. Art. No.:CD000402. DOI: 10.1002/14651858.CD000402.pub4.12 Weiderpass E, Adami HO, Baron JA, Magnusson C, Bergström R, Lindgren A, Corr
4. Endometrial cancer and oral contraceptives: an individual participant meta-analysis of 27 276 women with endometrial cancer from 36 epidemiological studies. Meta-Analysis Lancet Oncol. 2015 Sep;16(9):1061-1070. doi: 10.1016/S1470-2045(15)00212-0. Epub 2015 Aug 4.