Explaining The Link Between Breast Cancer And Pregnancy

It's all about estrogen.
Your breast cancer risk is lower if you get pregnant — but only if you get pregnant young.
Your breast cancer risk is lower if you get pregnant — but only if you get pregnant young.

There’s a ton of seemingly contradictory information out there about breast cancer and pregnancy. Getting pregnant will help keep you safe from breast cancer! Except when it won’t. Breastfeeding will also deter cancer! But it might hide your symptoms.

What exactly is going on here?

Shawn Chirrey, a senior manager of analysis at the Canadian Cancer Society, explained it’s all about estrogen.

“Estrogen is one of the main hormones associated with breast cancer,” he told HuffPost Canada. “It has an impact on the growth of breast cells, and experts believe it plays a role in the growth of breast cancer cells as well.”

Watch: 8 facts about breast cancer. Story continues after video.

What that means is that in most cases, the more pregnancies a woman has, the smaller her breast cancer risk.

“Pregnancy interrupts the exposure of breast cells to circulating estrogen,” because it lowers the amount of menstrual cycles you have, Chirrey explained.

But that only applies to women who get pregnant at a young age. Women who have children later than 30 are at the same risk as women who never get pregnant, because of the sustained estrogen exposure they’ve had throughout their life at that age.

And women who start menstruating younger than 12 or who enter menopause after about 55 will have a higher risk for the same reason, he said.

Breastfeeding can reduce the risk of breast cancer.
Breastfeeding can reduce the risk of breast cancer.

Breastfeeding also reduces exposure to estrogen, because in most cases, moms who breastfeed don’t get their periods while they’re doing it. So the longer you breastfeed, the greater protective effect there is against breast cancer, Chirrey said.

Similarly, women taking oral contraception — especially if it contains estrogen and progestin — are at a higher risk of breast cancer. So are people taking hormone replacement therapies — estrogen, for instance, is sometimes used to treat symptoms of menopause.

None of these factors mean women should feel they have to plan their pregnancies around the threat of cancer risk, or feel obligated to breastfeed, Chirrey said — they’re just things women should know about their bodies.

“We point them out just because the evidence is suggesting that,” he said, “but they’re not typically things that are modifiable.”

There are a variety of lifestyle factors that can be adapted to lessen breast cancer risk, including limiting alcohol intake and exercising regularly.

And cancer is so frequently unpredictable that even the people who on paper are the least likely to get the disease sometimes do. That was the situation HuffPost Canada’s news editor Michelle Friesen found herself in last year. She was young and healthy, and had breastfed both of her two children. But 18 months after the birth of her son, she was diagnosed with breast cancer.

Her doctor told her cancer was unlikely specifically because of her age and the fact that she had breastfed. But she ordered a mammogram and an ultrasound, just to be sure. The mammogram didn’t pick up on anything abnormal, but some tissue change detected in the ultrasound led to a biopsy, which led to the diagnosis.

Originally, her symptoms were attributed to mastitis, an inflammation in breast tissue that’s common in breastfeeding moms.

“I can’t decide if breastfeeding tried to kill me, or if it saved my life,” she previously told HuffPost Canada..

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