The Pill, pregnancy and cancer – making sense of the headlines

Are all ‘side effects’ bad for your health? In the case of the birth control Pill, it seems not.

Today, a study that we helped fund has confirmed that the combined Pill isn’t just an effective contraceptive, but that it also gives women long-lasting protection against ovarian cancer. Women who took the Pill for any length of time had a 14 per cent lower risk of ovarian cancer than those who never took it.

And women in the study who’d taken the Pill for 10 years were almost half as likely to develop ovarian cancer compared with women who’d taken it for less than 1 year. The below graphic shows how many women this equated to:

The study has been widely covered in the media, and these headline statistics are likely to be reassuring for the many thousands of women who take the Pill in the UK and across the world.

And women who have had kids also have reason to be positive – the study also confirmed that they have a reduced risk of ovarian cancer. Women in the study who’d been pregnant had their risk of ovarian cancer reduced by almost one-third (29 per cent), compared with women who hadn’t.

But what should an ‘average’ woman conclude from these numbers? Can any explicit advice be given based on the evidence?

Individual choice and personal circumstance

Clearly issues of contraception and pregnancy are extremely personal, and influenced by individual beliefs, as well as our wider society and culture. And broadly recommending, for instance, that women start having children to reduce their risk of ovarian cancer is clearly not an option.

Individual choice and circumstances are of course the main things behind whether or not a woman has children, and you could be forgiven if cancer risk isn’t top of your agenda when it comes to deciding whether or not to try for a baby.

But what about the Pill – should it be widely recommended for women to reduce their risk of ovarian cancer? Again, it’s a complex decision and one that each individual woman needs to discuss with her doctor. A few years ago we discussed evidence that the Pill could reduce the risk of several types of cancer.

Further studies have been published since then, but the issues we outlined still stand today – whilst the Pill significantly reduces a woman’s risk of ovarian cancer, it also increases a woman’s chances of developing other cancers – namely breast and cervical cancers. This makes recommending it for cancer prevention a difficult thing to do, and a blanket recommendation impossible.

Balancing risks and benefits

To help you understand how the Pill affects cancer risk, we’ve pulled together information from several studies to show how the Pill affects cancer risk over time:

The Pill and cancer risk (click to enlarge)

The graphic highlights that long-term use of the Pill not only reduces the risk of ovarian cancer, but also reduces the risk of womb cancer, to an even greater extent.

But the news is not all good. At the same time, the Pill also increases the risk of breast and cervical cancer.

The graphic also highlights a subtle but important distinction between the increased risks and the decreased risks – the protective effects of the Pill against ovarian and womb cancer last longer than its effects to increase risk of breast and cervical cancer.

To put it another way, if a woman has taken the Pill for 10 years then stops, within another decade her earlier increased risk of breast and cervical cancer will have dwindled away, whereas she will still be protected against ovarian and womb cancer.

What else affects ovarian cancer risk?

A woman’s chance of developing ovarian cancer is affected by a whole host of factors, not just the Pill and pregnancy. These include things like endometriosis, bodyweight, and smoking.

But everyone’s life is different, and every woman’s ovarian cancer risk will be influenced by a complex combination of her lifestyle and her genes. And the main cause of ovarian cancer is something none of us can control: age. Over 80 per cent of cases of the disease are in women over the age of 50 years.

The next graphic outlines some of the other factors that affect ovarian cancer risk:

Click to enlarge and for more detail

What to make of it all?

When it comes to cancer, there are some things that the evidence clearly points to. For instance, the relationship between smoking and cancer is unequivocal. Smoking is responsible for one in four cancer deaths in the UK.

Likewise, there’s a clear link between bodyweight and cancer – and ovarian cancer is more common among women who are overweight. So making sure you keep a healthy bodyweight and quit smoking are both good things to do if you are worried about your cancer risk.

Others recommendations need to be more subtly nuanced and made on an individual basis.

Your doctor can help you to make an informed choice about whether to use the Pill. This decision should first consider whether it’s a suitable form of contraceptive for you, and also account for the known risks and benefits of using the Pill, your lifestyle, your personal beliefs and preferences, and whether you have a strong family history of cancer or certain other diseases.

And while we’re talking of risk, let’s not forget what the Pill was designed to do: it’s 99.7 per cent effective at preventing unwanted pregnancies when used correctly – a benefit that must also be weighed against any potential risks.

Olly Childs

Reference

• Tsilidis, K. et al (2011). Oral contraceptive use and reproductive factors and risk of ovarian cancer in the European Prospective Investigation into Cancer and Nutrition British Journal of Cancer, 105 (9), 1436-1442 DOI: 10.1038/bjc.2011.371