What's the connection between obesity and breast cancer?

There are many different factors that can elevate your risk of developing breast cancer. Some of these are uncontrollable, such has having a mutation on the BRCA1 or BRCA2 gene or having dense breasts.

Others are considered controllable, such as how much you exercise and whether you eat a balanced, nutritious diet. Obesity, or being overweight, is one such "lifestyle factor" that many doctors consider to be a controllable risk factor for developing breast cancer that can also impact mortality rates.

The World Health Organization defines overweight and obesity as "abnormal or excessive fat accumulation that may impair health." Using the simple calculation of weight-for-height known as the body mass index, adults with a BMI greater than or equal to 25 are said to be overweight, while adults with a BMI greater than or equal to 30 are considered obese. (You can calculate your own BMI with this online calculator from the National Heart, Lung and Blood Institute.)

[See: 10 Things You Didn't Know About Breast Cancer.]

RELATED: 10 celebrities get real about breast cancer

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10 celebrities get real about breast cancer

Julia Louis-Dreyfus

The 56-year-old was most recently diagnosed with breast cancer soon after the 2017 Emmy Awards. She confirmed the diagnosis on Instagram, quickly calling attention to the plight of other women who don't have health care. 

"1 in 8 women get breast cancer. Today, I'm the one. The good news is that I have the most glorious group of supportive and caring family and friends, and fantastic insurance through my union. The bad news is that not all women are so lucky, so let's fight all cancers and make universal health care a reality," she wrote in the post

Angelina Jolie 

In 2013, at age 37, the actress wrote a New York Times piece about her experiences with breast cancer and the BRCA1 gene. She had an 87% risk of breast cancer, 50% risk of ovarian cancer, so she took preventative action, including a double mastectomy and the later removal of her ovaries and fallopian tubes.

"Once I knew that this was my reality, I decided to be proactive and to minimize the risk as much I could. I made a decision to have a preventive double mastectomy. I started with the breasts, as my risk of breast cancer is higher than my risk of ovarian cancer, and the surgery is more complex," she wrote.

Continuing in the New York Times, But I am writing about it now because I hope that other women can benefit from my experience. Cancer is still a word that strikes fear into people’s hearts, producing a deep sense of powerlessness. But today it is possible to find out through a blood test whether you are highly susceptible to breast and ovarian cancer, and then take action.

  

Cynthia Nixon

At 40, the acclaimed actress was diagnosed with breast cancer after a routine mammogram in 2006. She decided to keep it private for a year after her diagnosis. 

At age 12, Nixon watched her mother battle breast cancer and knew the importance of preventative care. 

"I’ve learned that if you catch breast cancer early, the chances are overwhelmingly good that you’ll be cured. So my attitude, which very much mirrored my mother’s, was this wasn’t a big deal," the star said, according to Marie Claire

Giuliana Rancic 

In 2011, after the diagnosis of an early-stage tumor, the host underwent a double mastectomy and reconstructive surgery.

She said to Glamour: "....My doctor said, "We have great news in one breast and bad news in the other. You need to start thinking about a mastectomy." That had been the furthest thing from my mind. I knew nothing about breast cancer before this happened to me, and I thought mastectomy meant stage three or four cancer. I didn't have a big family history of it. I just never thought it would happen to me. I really didn't."

Shannen Doherty

The former "Beverly Hills, 90210" star was diagnosed in 2015 and regularly documented her battle on social media. After going through chemotherapy, she announced she's in remission in April 2017. 

"Moments. They happen. Today was and is a moment. What does remission mean? I heard that word and have no idea how to react. Good news? YES. Overwhelming. YES. Now more waiting. As every single one of my fellow cancer family knows, the next five years is crucial. Reoccurrences happen all the time," she shared on social media

Sheryl Crow

In 2006, the singer publicly announced she was battling the disease after she underwent "minimally invasive surgery." 

"I am inspired by the brave women who have faced this battle before me and grateful for the support of family and friends," she said according to ABC News

Olivia Newton-John

In 2017, the 68-year-old singer and actress revealed she was once again battling breast cancer. After her first diagnosis in 1992, she underwent a partial mastectomy as well as chemo. 

"I am really grateful for and touched by the worldwide outpouring of love and concern. Thank you. I am feeling good and enjoying total support from my family and friends, along with a team of wellness and medical practitioners both here in the US and at my Olivia Newton-John Cancer Wellness and Research Centre in Melbourne, Australia. I’m totally confident that my new journey will have a positive success story to inspire others!” she said exclusively to People in June

Melissa Etheridge

Because of the singer's family history, Etheridge was "vigilant" about examinations before eventually being diagnosed in 2004. 

"I am the healthiest I have ever been in my life. It excites me every day when I can wake up and feel energy and feel good and feel purpose. The changes I made were big and not easy. Sugar is a drug, incredibly addictive. That one change can make a huge difference in your life," she said to ABC News in 2015

Christina Applegate

At 36 years old, the actress was diagnosed with breast cancer in 2008. After biopsies and a lumpectomy, as well as radiation, she tested positive for the BRCA gene.

Later, she underwent a double mastectomy. "It came on really fast. It was one of those things that I woke up and it felt so right," she says. "It just seemed like, 'I don't want to have to deal with this again. I don't want to keep putting that stuff in my body. I just want to be done with this.' & I was just going to let them go," she said according to CNN.

Rita Wilson

In 2015, it became known that the actress was battling breast cancer and underwent both a double mastectomy and reconstructive surgery. 

Since then, she's been outspoken about encouraging others to be vigilant about routine checks.

"Last week, with my husband by my side, and with the love and support of family and friends, I underwent a bilateral mastectomy and reconstruction for breast cancer after a diagnosis of invasive lobular carcinoma. I am recovering and most importantly, expected to make a full recovery. Why? Because I caught this early, have excellent doctors and because I got a second opinion," she said according to People

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According to WHO estimates, 1.9 billion adults age 18 and older – some 39 percent of the world's adult population – were overweight in 2016. Of them, 650 million people or about 13 percent of the adult population (11 percent of men and 15 percent of women) worldwide were obese in 2016.

Meanwhile, figures from the Centers for Disease Control and Prevention indicate that 70.7 percent of American adults over age 20 are overweight, and 37.9 percent of American adults over age 20 are obese.

Clearly, being too heavy is a global phenomenon, and being overweight or obese has been associated with a number of other chronic health problems including heart disease, diabetes and cancer.

The connection between a high BMI and breast cancer specifically is well-established. A high BMI has been isolated as a risk factor for developing the disease for many years, but more recently it's been noted as impacting mortality rates. A 2014 review study in Annals of Oncology indicated that "in breast cancer survivors, higher BMI is consistently associated with lower overall and breast cancer survival, regardless of when BMI is ascertained."

RELATED: What Foods You Should Eat or Avoid to Prevent Breast Cancer

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What Foods You Should Eat or Avoid to Prevent Breast Cancer

Prevent breast cancer by adopting a healthy lifestyle. Whether they contain body-boosting antioxidants or powerful micronutrients, these 13 foods are linked to lower breast cancer risk. Plus, find out what foods you should avoid.

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Flaxseed

According to flaxseed researcher Dr. Lilian Thompson, PhD from the Unversity of Toronto, research suggests that flaxseed may reduce the risk of breast cancer. Flaxseed contains plant omega-3 fatty acid ALA and lignans, which both inhibit tumor growth, as well as protective antioxidants.

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Oily Fish

A recent study in the British Medical Journal found that women who ate the highest levels of omega-3 fatty acids from fish had a 14 percent lower risk of breast cancer compared to women who consumed the least. Oily fish like salmon and tuna are great sources of omega-3 fatty acids.

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Cruciferous vegetables

Vegetables in the cabbage family like broccoli, cauliflower and Brussels sprouts can protect against estrogen-dependent cancers. In addition to being a good source of carotenoids and fiber, cruciferous vegetables naturally contain chemicals called glucosinolates, which are known for their anticancer effects.

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Walnuts

Walnuts, which have anti-inflammatory health benefits, have been linked to a reduced risk of breast cancer in animal studies.

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Dark green, leafy vegetables

Leafy greens like spinach, kale, broccoli and collard greens are significant sources of carotenoids, a micronutrient linked to reduced breast cancer risk. Researchers at Harvard Medical School found that women who consumed high levels of carotenoids had 15-20 percent lower risk of breast cancer compared to women who ate the lowest levels.

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Red, Yellow and Orange Vegetables

Other sources of carotenoids include vibrant vegetables like sweet potatoes, carrots and squash. Science suggests eating foods high in this micronutrient may reduce your risk of breast cancer.

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Green Tea

Researchers from Columbia University Medical Center found the consumption of green tea extract to inhibit two growth factors that promote tumor cell growth among women with breast cancer. The polyphenols in green tea may explain these anti-cancer properties.

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Whole Grains

Research suggests that diets high in fiber can lower your risk of breast cancer by reducing the levels of estrogen in blood. Whole grains are an excellent source of fiber, as well as beans, brown rice and oatmeal.

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Seaweed

Varieties of seaweed like nori, kombu and wakame are high in cancer-fighting carotenoids. Sprinkle shreds of seaweed on top of salads and soups.

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Extra Virgin Olive Oil

Studies suggest that the natural antioxidants in good-quality extra virgin olive oil may help fight breast cancer by suppressing the expression of cancer genes. The oil is pressed without heat or chemical treatments, thereby preserving valuable phytonutrients.

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Parsley

University of Missouri researchers found that a compound called apigenin, commonly found in parsley and other plants, stopped or slowed down tumor formation in rats with a certain type of breast cancer. Try mincing parsley on top of your dishes for a healthy boost.

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Folic Acid-Rich Foods

One study found that folate, a vitamin found in dark green leafy vegetables and citrus fruits, can mitigate the adverse effects of alcohol consumption on breast cancer risk, according to the American Cancer Society. Another good way to get folic acid is by taking a daily multivitamin.

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Peanut Butter

A study published in Breast Cancer Research and Treatment last month found a link between regular peanut butter consumption in childhood and a decreased risk of developing benign breast disease, which is a known risk factor for breast cancer. While it's too early to suggest that peanut butter lowers breast cancer risk, it doesn't hurt to swap junk food with all-natural peanut butter-topped veggies and nuts at the kids' snack time.

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Avoid these foods that are linked to an increased risk of breast cancer.

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Alcohol

You'd be surprised to find that even a little alcohol consumption can be unhealthy. According to the American Cancer Society, even a few alcoholic drinks a week may increase the risk of breast cancer in women.

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High-fat Dairy Food

U.S. News reports that even as little as one serving of high-fat dairy foods per day can increase the risk of breast cancer by nearly 50 percent, according to a study published in the Journal of the National Cancer Institute. Foods like whole milk and cream are considered high-fat dairy products.

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Red Meat

Researchers from the University of Leeds found that women who consumed red meat every day had a 56 percent greater risk of breast cancer than women who ate no red meat, stressing the importance of eating this protein in moderation.

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Processed Meat

Processed meats, like bacon, sausage and ham, are also on the chopping block. The same study revealed women who consumed these foods often had a 64 percent greater risk of breast cancer than those who ate none.

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Sugar

While sugar consumption has not been directly linked to breast cancer risk, eating unhealthily can promote obesity, which is associated with higher breast cancer risk. Limit your intake of cakes, cookies, sweetened cereals, sugary beverages and other sweets.

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The findings also indicated that when compared with normal-weight women, obese women had a 21 to 41 percent higher risk for total mortality and a 25 to 68 percent increased risk for breast cancer mortality, depending on how much time had passed since their breast cancer diagnosis. The study recommended that maintaining a BMI of between 18.5 and 24.9 is best for survival.

[See: 10 Medical Services Medicare Doesn't Cover.]

But why does being overweight contribute to the development of cancer? Scientists are still figuring out the exact mechanism, but it seems there's a connection among fatty tissue, hormones and inflammation.

Part of the problem is likely due to the fact that adipose tissue, or fat, "secretes a lot of hormones and is part of the metabolism of the body. Adipose tissue is probably the largest endocrine organ in the body," says Dr. Sagar Sardesai, assistant professor of medicine at the Stefanie Spielman Comprehensive Breast Center at The Ohio State University Wexner Medical Center.

In a lean patient, this process is in balance, so it does not typically pose an issue. But in an overweight patient, an increase in circulating hormones can lead to inflammation, and this inflammation could lead to cancer developing. "As the [amount of] adipose tissue goes up and grows larger, it often gets what I call angry," or inflamed. Inflammation is associated with cancer, so the more inflammation in the body, the better the chances that cancer could develop.

RELATED: Warning signs and risk factors of breast cancer

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Risk factors of breast cancer: obesity

(Photo via Getty Images)

Risk factors of breast cancer: lack of exercise

(Photo by Martin Barraud, Getty Images)

Risk factors of breast cancer: alcohol use

(Photo via Ron Chapple Stock, Getty Images)

Risk factors of breast cancer: an unhealthy diet

(Photo by Dean Belcher, Getty Images)

Risk factors of breast cancer: smoking

(Photo via Getty Images)

Common signs of breast cancer: a breast mass that is hard and/or irregular 

(Photo via Getty Images)

Common signs of breast cancer: changes in the skin of the breast such as puckering, irritation, scaling, dimpling, redness or thickening

(Photo via Getty Images)

Common signs of breast cancer: swelling of all or part of the breast, even with no specific lump

(Photo via Getty Images)

Common signs of breast cancer: enlargement or swelling of the lymph nodes in the armpit area

(Photo via Getty Images)

Common signs of breast cancer: nipple discharge, that is not breast milk

(Photo via Ron Chapple Stock, Getty Images)

Common signs of breast cancer: nipple retraction, which looks like a turning inward of the nipple

(Photo via Getty Images)

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Dr. Neil Iyengar, a medical oncologist focusing on patients with breast cancer at Memorial Sloan Kettering Cancer Center in New York, explains the series of steps in which the growth of fatty tissue may lead to inflammation that could subsequently trigger cancer.

"The fatty tissue is a very active tissue, and it serves the purpose of maintaining homeostasis and ensuring that all of our metabolic processes are in order," he says. But it needs an adequate blood supply to conduct these activities, and as it expands, it can outgrow this supply.

"As soon as we put on too much fat or the fat tissue outgrows its blood supply and nutrition support, then that tissue becomes diseased and can no longer fulfill its multiple functions of maintaining metabolic homeostasis," he says. He says the fat cells die, and then the immune system tries to clear the dead cells out. But that's difficult to do because fat cells are among the largest cells in the body, "so it becomes an inefficient process."

This can lead to hormones being produced, including estrogen precursors that can directly stimulate the growth of breast cancer tumors. "But in addition to hormones, you have secretion of inflammatory molecules that can stimulate tumor growth. It's inflammation in a diseased fat pad that is leading to the building blocks, so to speak, that allows tumors to overtake that process and start to grow," Iyengar says.

RELATED: Celebrities who have publicly battled breast cancer

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Toronto, Canada - September, 17 2015 - Actress Cynthia Nixon (best known for Sex and the City) was in Toronto promoting her indie film JAMES WHITE. TIFF15, Toronto International Film Festival September 17, 2015 (Richard Lautens/Toronto Star via Getty Images)
Sheryl Crowe arrives at the 2014 Vanity Fair Oscar Party on March 2, 2014 in West Hollywood, California. (Photo credit ADRIAN SANCHEZ-GONZALEZ/AFP/Getty Images)
LOS ANGELES, CA - AUGUST 01: Christina Applegate arrives at Dizzy Feet Foundation's 5th Annual Celebration Of Dance Gala held at Club Nokia on August 1, 2015 in Los Angeles, California. (Photo by Michael Tran/FilmMagic)
Actress Maura Tierney of Showtime's 'The Affair' poses in the Getty Images Portrait Studio powered by Samsung Galaxy at the 2015 Summer TCA's at The Beverly Hilton Hotel on August 10, 2015 in Beverly Hills, California. (Photo by Maarten de Boer/Getty Images)
US actress and UNHCR ambassador Angelina Jolie stands during a visit to a camp for displaced Iraqis in Khanke, a few kilometres (miles) from the Turkish border in Iraq's Dohuk province, on January 25, 2015. Run by authorities from the three-province autonomous Kurdish region of north Iraq with the help of the United Nations refugee agency, the UNHCR, Khanke aims to house 18,000 people, said the agency's Liena Veide. AFP PHOTO/SAFIN HAMED (Photo credit should read SAFIN HAMED/AFP/Getty Images)
LOS ANGELES, CA - AUGUST 13 NBCUNIVERSAL EVENTS -- NBCUniversal Portrait Studio, August 2015 -- Pictured: TV personality Giuliana Rancic from 'Fashion Police' poses for a portrait at the NBCUniversal Summer Press Day during the 2015 Summer TCA Tour at The Beverly Hilton on August 12, 2015 in Beverly Hills, California. (Photo by: Christopher Polk/NBC/NBCU Photo Bank via Getty Images)
SIMI VALLEY, CA - JULY 05: Nancy Reagan attends The Grand Opening of D23 Presents Treasures of The Walt Disney Archives on July 5, 2012 in Simi Valley, California. (Photo by Michael Kovac/FilmMagic)
BEVERLY HILLS, CA - MAY 24: Reporter Linda Ellerbee speaks during the 36th Annual Gracie Awards Gala at the Beverly Hilton Hotel on May 24, 2011 in Beverly Hills, California. (Photo by Frederick M. Brown/Getty Images)
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This process is similar to how a wound heals, Iyengar says. "The obese fat pad is a dysfunctional fat pad that is inflamed. On a molecular level, it resembles a healing wound because there are inflammatory molecules, there's collagen being laid down, fibrous tissue being laid down and there are new blood vessels that are trying to develop. A healing wound is good when you're trying to heal a trauma that happens in an acute setting, but chronically, that kind of situation can lead to tumor development," he says.

[See: 7 Innovations in Cancer Therapy.]

No matter what the exact pathway is, the moral of the story is to try to keep your weight at a healthy level. More specifically, it's important to keep your fat levels in check all through life. Diet and exercise are the best tools with the fewest side effects currently available to control your weight, so speak with your doctor or a nutritional counselor about the best ways to maintain a healthy weight and activity level for the long term.

And keep in mind that maintaining that healthy weight becomes both more important and more difficult as we age. Gaining weight is a common phenomenon as the body changes with age. For women, menopause, which occurs on average at age 51, is a particular point of challenge that causes many to gain weight. The earliest stages of menopause, called perimenopause, can start when a woman is still in her 40s.

RELATED: Build A Breast Cancer-Fighting Menu

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What should you put on your plate? Experts recommend the following...

Five Fruits And Veggies

Eat five or more servings of a variety of colorful vegetables and fruits every day. Don’t be shy with produce: Both the Centers for Disease Control and Prevention and the National Cancer Institute recommend up to 13 servings, or 6½ cups, of fruits and vegetables a day to keep us slim and to fight a range of diseases.

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Whole Grains

Choose whole grains over processed (refined) grains for extra fiber to spur weight loss; these will help steady your blood sugar levels as well, and avoid insulin resistance, which can lead to diabetes.

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A Low-Fat Diet

Follow a low-fat diet. Studies link a high-fat diet to more aggressive forms of breast cancer. A low-fat diet — one where 30 percent or less of your calories come from fat — also helps prevent recurrence. Choose foods with healthy fats for an extra brain- and heart-health boost: Opt for fish and nuts, for instance, over fried foods and those high in saturated fat.

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Antioxidants

Get antioxidants from fruits and vegetables, not supplements. Antioxidants are nutrients — namely vitamins C and E, carotenoids and other plant compounds (phytochemicals) — that protect against cell damage that may lead to cancer. Research has shown that people who eat lots of produce, a naturally rich source of antioxidants, have a lower risk for certain cancers but that antioxidant supplements (which contain high concentrations of specific nutrients) do not reduce risk.

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Avoid Alcohol

Drink no more than one alcoholic beverage per day. Some studies indicate that less — or none at all — is best for breast cancer protection. Women with estrogen-receptive breast cancer should avoid alcohol altogether due to its potential effect on estrogen. If you do drink, make sure you get adequate folic acid, or folate. Too little of this B vitamin may increase the risk of breast cancer, especially in women who drink alcohol. Leafy greens, beans, whole grains and fortified cereals are all good sources.

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Avoid Fried Food

Limit intake of meats that have been fried, barbecued, cooked well-done, preserved (by smoking or salting) or processed (like deli meats that contain nitrates). These cooking methods are linked to heightened breast cancer risk.I

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Tea

Some studies show that people who drink green tea, and to a lesser extent black tea, which is high in a type of antioxidant called polyphenols, have lower cancer risk. But researchers don’t know if the cancer protection comes from drinking tea itself or if tea drinkers have other healthy habits that reduce their risk. (Caffeine may worsen symptoms of fibrocystic breast lumps in some women, but there is no evidence that it increases the risk of breast cancer.)I

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Organic Food

Though it is an area of debate and strong personal views, there is no conclusive evidence that eating organic reduces cancer risk. However, there may be other reasons you want to eat organic food, and it certainly won’t increase your risk.

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Vitamin D And Calcium

High levels of vitamin D and calcium may offer some protection against the most aggressive kinds of breast cancer but only in premenopausal women, emerging research shows.

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"Weight gain in the years leading up to menopause is especially [problematic], particularly for estrogen-sensitive breast cancers," Sardesai says. It also gets a lot harder to shed excess pounds after menopause. So keep an eye on the scale as you go, and hopefully you can keep the pounds at bay now to help reduce your risk of developing breast cancer or improve your outlook later.

Copyright 2017 U.S. News & World Report

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