Every pregnancy helps reduce endometrial cancer risk

New QIMR Berghofer research has found each additional pregnancy a woman experiences, including those that result in miscarriage, can help reduce her risk of developing endometrial cancer.

The research led by the head of QIMR Berghofer Medical Research Institute's Gynecological Cancers group, Professor Penelope Webb, found the risk continued to drop with each pregnancy, even up to as many as eight pregnancies.

Professor Webb said the study findings provided new insight into endometrial cancer, which is estimated to be the 5th most common cancer diagnosed among Australian women.

"It's well known that having a full-term pregnancy reduces a woman's risk of developing endometrial cancer, but our research has shown that not only does each additional full-term pregnancy reduce that risk by about 15 percent, the reduction continues for up to at least eight pregnancies," Professor Webb said.

"We have also clearly shown for the first time that pregnancies that end in a miscarriage also reduce risk of endometrial cancer by about seven percent. Unlike many other cancers, endometrial cancer rates are increasing so it is vital that we get a better understanding of the factors that affect a woman's risk. If scientists can understand what drives endometrial cancer, there's hope that we may be able to prevent women from developing it in the future."

The researchers examined pregnancy data from 30 studies conducted around the world, including Australia, held by the Epidemiology of Endometrial Cancer Consortium. This included 16,986 women with endometrial cancer and 39,538 women who have never had the disease.

First author, Associate Professor Susan Jordan who is now at the University of Queensland School of Public Health, said the study findings raised questions about the commonly held belief that hormone levels in the last trimester provide the protective effect against women's cancers.

"Our analysis in this large group of women shows that while a full-term pregnancy is associated with the greatest reduction in risk for endometrial cancer, even pregnancies that end in the first or second trimester appear to provide women with some protection," Associate Professor Jordan said.

"This suggests that very high progesterone levels in the last trimester of pregnancy is not the sole explanation for the protective effect of pregnancy. If women who experience miscarriage have a seven to nine percent reduced risk of endometrial cancer then early pregnancy factors may also be playing a protective role against this disease. This raises the need for more research to identify other factors that underlie this protective effect."

The researchers found women who had only boys or a mix of boys and girls had a lower risk of endometrial cancer compared to mothers of only girls.

There was also no extra benefit from twin or multiple births.

Endometrial cancer is the most common cancer of the uterus. Cancer Australia estimates it affected about 3,115 women in 2019 and claimed about 350 lives in 2018.

The study findings have been published in the International Journal of Cancer.