Some hormonal contraceptives take the form of implants under the skin. WiP-Studio/Shutterstock^[6]

How does the contraceptive pill affect cancer risk?

The International Agency for Research on Cancer^[7], which compiles evidence on cancer causes, has concluded^[8] that oral contraceptives have mixed effects on cancer risk.

Using the oral contraceptive pill:

• slightly increases your risk of breast and cervical cancer in the short term, but
• substantially reduces your risk of cancers of the uterus and ovaries in the longer term.

Our earlier work showed the pill was responsible for preventing far more cancers overall than it contributed to.

In previous research^[9] we estimated that in 2010, oral contraceptive pill use prevented over 1,300 cases of endometrial and ovarian cancers in Australian women.

It also prevented almost 500 deaths^[10] from these cancers in 2013. This is a reduction of around 25% in the deaths that could have occurred that year if women hadn’t taken the pill.

In contrast, we calculated the pill may have contributed to around 15 deaths from breast cancer^[11] in 2013, which is less than 0.5% of all breast cancer deaths in that year.

Previous work showed the pill was responsible for preventing far more cancers overall than it contributed to. Image Point Fr^[12]

What about long-acting reversible contraceptives and cancer risk?

Long-acting reversible contraceptives^[13] – which include intrauterine devices or IUDs, implants under the skin, and injections – release progesterone-like hormones.

These are very effective contraceptives that can last from a few months (injections) up to seven years (intrauterine devices).

Notably, they don’t contain the hormone oestrogen, which may be responsible for some of the side-effects of the pill (including perhaps contributing to a higher risk of breast cancer).

Use of these long-acting contraceptives has doubled over the past decade^[14], while the use of the pill has declined. So it’s important to know whether this change could affect cancer risk for Australian women.

Our new study^[15] of more than 1 million Australian women investigated whether long-acting, reversible contraceptives affect risk of invasive cancers. We compared the results to the oral contraceptive pill.

We used de-identified health records for Australian women aged 55 and under in 2002.

Among this group, about 176,000 were diagnosed with cancer between 2004 and 2013 when the oldest women were aged 67. We compared hormonal contraceptive use among these women who got cancer to women without cancer.

We found that long-term users of all types of hormonal contraception had around a 70% lower risk of developing endometrial cancer in the years after use. In other words, the risk of developing endometrial cancer is substantially lower among women who took hormonal contraception compared to those who didn’t.

For ovarian cancer, we saw a 50% reduced risk (compared to those who took no hormonal contraception) for women who were long-term users of the hormone-containing IUD.

The risk reduction was not as marked for the implants or injections, however few long-term users of these products developed these cancers in our study.

As the risk of endometrial and ovarian cancers increases with age, it will be important to look at cancer risk in these women as they get older.

What about breast cancer risk?

Our findings suggest that the risk of breast cancer for current users of long-acting contraceptives is similar to users of the pill.

However, the contraceptive injection was only associated with an increase in breast cancer risk after five years of use and there was no longer a higher risk once women stopped using them.

Our results suggested that the risk of breast cancer also reduces after stopping use of the contraceptive implants.

We will need to follow-up the women for longer to determine whether this is also the case for the IUD.

It is worth emphasising that the breast cancer risk associated with all hormonal contraceptives is very small.

About 30 in every 100,000 women aged 20 to 39 years develop breast cancer each year, and any hormonal contraceptive use would only increase this to around 36 cases per 100,000.

What about other cancers?

Our study did not show any consistent relationships between contraceptive use and other cancers types. However, we only at looked at invasive cancers (meaning those that start at a primary site but have the potential to spread to other parts of the body).

A recent French study^[16] found that prolonged use of the contraceptive injection increased the risk of meningioma (a type of benign brain tumour).

However, meningiomas are rare, especially in young women. There are around two cases in every 100,000^[17] in women aged 20–39, so the extra number of cases linked to contraceptive injection use was small.

The French study found the hormonal IUD did not increase meningioma risk (and they did not investigate contraceptive implants).

Benefits and side-effects

There are benefits and side-effects for all medicines, including contraceptives, but it is important to know most very serious side-effects are rare.

A conversation with your doctor about the balance of benefits and side-effects for you is always a good place to start.

Read more https://theconversation.com/long-acting-contraceptives-seem-to-be-as-safe-as-the-pill-when-it-comes-to-cancer-risk-new-study-246028