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Women with three children less likely to develop endometrial cancer, University of Queensland study finds

Denise Marriott felt perfectly well and healthy, but a minor symptom told her something might be off. 

The 67-year-old trusted her gut and visited her doctor for a check-up a week ago, which led to a series of pelvic exams and pathology tests.

"I had absolutely no pain whatsoever. No other symptoms. I simply acted on the one that occurred to me," she said.

Within a matter of days, Ms Marriott found out she had a common form of cancer growing on the lining of her uterus and had an operation to immediately remove it.

"I wasn't expecting that, so it was a bit of shock," she said.

"But I am one of the very, very lucky ones. I've just heard from [my surgeon] that I won't have to undergo chemotherapy or radiation."

Ms Marriott's diagnosis comes at the same time that a new peer-reviewed study has found women who have three babies are up to 50 per cent less likely to develop endometrial cancer than women who have none.

Researchers from the University of Queensland's Institute for Molecular Bioscience said it was the first genetic study to analyse multiple risk factors for endometrial cancer at once and it could advance the development of preventative therapies.

The use of genetic data from up to 700,000 women allowed researchers to separate some known risk factors, such as increased body mass index (BMI) and age at first menstruation, to specifically look at the effect of the number of births.

Endometrial cancer affects the endometrium – the lining of the uterus or womb – and is the fifth most common cancer for Australian women.

Dr Gunn-Helen Moen, who is the senior author of the research, said while it was previously assumed there was a link between childbirth and the lower risk of developing endometrial cancer, the new findings confirm the causal relationship.

"We found that the more time a woman spent pregnant or on the contraceptive pill – when the body is exposed to less estrogen – was associated with a lower risk endometrial cancer," she said.

Dr Moen said a possible explanation for this outcome is that high levels of the estrogen hormone are a risk factor for women.

"Pregnancy and the contraceptive pill both provide progesterone to oppose estrogen, and this could be why we see a protective effect against this cancer," she said.

"To put it simply, the shorter the exposure to estrogen over your lifetime, the smaller your risk of endometrial cancer," she said.

Study not a sign to 'have an extra child'

Dr Moen said it was also possible the body expels pre-cancerous cells from the uterus during childbirth, but further research would be needed to determine whether it is the hormonal or mechanical effects of pregnancy that have a more protective effect.

"I think it would be very interesting if we could find cohorts that have data on the exact duration of taking the contraceptive pill, and the type of contraceptive pill taken, to see whether or not there is actually a causal decrease in risk," she said.

Dr Moen said these findings would be useful for screening women who are at a higher risk of developing endometrial cancer.

"I also think it might be one step on a long road to finding some therapies," she said.

"The study is more useful for working out how we can reduce the risk of endometrial cancer, rather than to tell people they have to have an extra child."

'Amazing benefits' of childbirth

For Sunshine Coast mother-of-three, Emma Read, the 50 per cent reduced risk of developing endometrial cancer was "incredible" news.

"Honestly, I had no idea and I think it's amazing [childbirth] has such a good benefit," she said.

"It's great to know because I think when you are planning to have children, you are more aware of the risks and the health impacts of having children."

The 39-year-old said she hopes further research into whether the contraceptive pill could help women reduce their risk of endometrial cancer could be of benefit to her daughters one day.

"For so long, especially in my 20s, we didn't talk about women's health and certainly not about endometrial cancer," she said.

"I think the more that we break down that barrier, make it accessible, and have those conversations, the better.

"Fingers and toes crossed that it's something that my daughter can look into in her 20s because that's what we're thinking about – it's about that next step and future generations."

Following her own experience, Ms Marriott said her health advice to other women would be to listen to their body and act on it quickly.

"Trust your own instincts, even if it might seem mere or it's a small thing that can easily be brushed to the side," she said.

"If you don't do anything about it and then later on something happens, you'll kick yourself constantly."

The research was published this month in the journal BMC Medicine. 

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