Breast cancer is the second-most common cancer diagnosed in women, but it's not all bad news. For starters, this cancer is being caught earlier than ever thanks to annual mammograms starting at age 40.

"Breast cancer is becoming more and more curable, but early detection is the key to this," says Dr. Priya Ramshesh, a medical oncologist at Houston Methodist.

We also know a lot more about breast cancer these days, including the factors that make developing it more likely. Knowing these breast cancer risk factors can help you understand how to reduce your risk and whether you might need earlier screening.

What are the known risk factors for breast cancer?

Having a family history is likely the breast cancer risk factor we hear about the most, but it's not the only one to be aware of.

The factors that increase breast cancer risk include:

• Being female
• Increasing age
• Certain genetic mutation(s) linked to breast cancer, like BRCA1 and BRCA2
• Personal history of radiation therapy to the chest area (usually the result of undergoing lymphoma treatment as a child, teen or young adult)
• Family history of breast cancer or conditions linked to breast cancer
• Starting your menstrual cycle before age 12
• Experiencing menopause after age 55
• Being overweight, especially having excess weight around the waistline (also known as visceral fat)
• Poor diet, since this can contribute to weight gain
• Lack of physical activity, since this can contribute to weight gain
• Long-term use of hormone replacement therapy
• Never having been pregnant
  
  

Having one or more of these risk factors doesn't mean you'll get breast cancer, just as having none doesn't mean you won't get it. This is simply a list of what's known to be associated with an increased chance of eventually developing this particular type of cancer.

"The biggest risk factors for breast cancer are being a woman and getting older," says Dr. Ramshesh. "These are factors we can't change, of course, and it's why annual mammograms are recommended for every woman starting at age 40."

A few other factors on this list also can't be changed — though that doesn't mean they can't be addressed. Additionally, some factors can be modified, meaning there are things any woman can do to reduce her chances of developing breast cancer.

Certain breast cancer risk factors can't be changed

In addition to age and being female, you can't change when your menstrual period started or when you go through menopause — but that said, these factors don't affect how you approach reducing your risk of breast cancer or screening for it. If anything, these non-modifiable risk factors just reiterate the importance of controlling what you can, like living a healthy lifestyle and being committed to getting annual mammograms starting at age 40.

Some of the other breast cancer risk factors you can't change may require action, though. For instance, undergoing chest radiation or having a gene mutation linked to breast cancer warrants earlier screening, sometimes at a young age and as early as 25.

"About 10% of breast cancers are associated with a genetic risk," adds Dr. Ramshesh. "It's why knowing family history is important, since it can be a starting point to perhaps getting some testing done."

That said, having a family member who has breast cancer, or had it in the past, doesn't automatically mean you're at higher risk. Dr. Ramshesh points out that more information is needed.

"How many family members have had breast cancer? Were any of them younger than 50 at the time of diagnosis?" Dr. Ramshesh asks. "Do other conditions linked to breast cancer, like ovarian cancer, also run in the family?"

These are all questions that can help your doctor determine whether hereditary risk exists and if you might benefit from genetic testing. If a genetic mutation linked to breast cancer is found, your doctor will recommend earlier and more frequent breast cancer screening. (Related: Breast Cancer Screening: Who Needs a Mammogram Before Age 40?)

“The goal is to find the mutation in women before they develop cancer,” Dr. Sandra Templeton, breast surgeon at Houston Methodist says. “A simple blood or saliva test is meant to tell a woman whether she’s at high risk.”

While not a risk factor for breast cancer, breast density is something you can't change that can make breast cancer harder to catch.

"Mammograms are the gold standard for detecting breast cancer early, but dense breast tissue can make interpreting a mammogram challenging," explains Dr. Ramshesh. "Dense breast tissue can obscure small masses on a mammogram."

This doesn't mean an annual mammogram isn't important for people with dense breasts, though.

"Keep your regular exams going and, if you have dense breasts, just know that the radiologist may recommend adding a supplemental ultrasound," says Dr. Ramshesh.

Some breast cancer risk factors are modifiable

In terms of the breast cancer risk factors that are in your control, there's an underlying principle to understand: The more estrogen a person is exposed to, the greater their breast cancer risk.

Estrogen exposure isn't always modifiable, of course — that you can't change the fact you started your period early or went through menopause late — but certain lifestyle choices influence estrogen levels beyond the ebbs and flows of your menstrual cycle.

"Weight gain is a big one, particularly weight gain after menopause since it becomes easier to gain weight at this point in a woman's life," explains Dr. Ramshesh. "The fat tissue allowed to deposit in the liver, the more cholesterol in that tissue that will be converted to estrogen — adding to your breast cancer risk."

Another risk factor to consider is hormone therapy, a common treatment for menopause symptoms like hot flashes and night sweats. Long-term hormone therapy, which involves taking a low dose of estrogen, has been linked to breast cancer.

"Have an informed discussion with your healthcare provider so you understand the potential risks of hormone therapy," adds Dr. Ramshesh.

How to reduce breast cancer risk

All women are at risk for breast cancer, so it's important for all women to take steps to reduce that risk, such as:

• Learning about your family's health history, since this can help determine whether you might need breast cancer screening before age 40
• Maintaining a healthy weight and understanding the danger that visceral fat imposes
• Eating a healthy diet, choosing vegetables, fruits, whole grains, low-fat dairy products and lean proteins over fatty meats and processed foods full of refined grains, saturated fats and added sugars
• Avoid drinking alcohol excessively
• Being physically active — the American Cancer Society, for instance, recommends at least 30 minutes of exercise at least five times per week
  
  

"It's very important to have an informed discussion with either your gynecologist or primary care doctor about your family history, especially in terms of genetic risk," says Dr. Ramshesh. "It's not just a history of breast cancer to take into account, there are more subtle links to consider — such as history of ovarian cancer, male breast cancer, colon cancer or Lynch syndrome."

Lastly, while not a way to prevent breast cancer, Dr. Ramshesh reminds us that following breast cancer screening guidelines is imperative, since being an aging woman is a risk we'll all eventually classify for.

"Get your mammogram each year starting at age 40," reiterates Dr. Ramshesh. "Don't put this screening off. There is a little discomfort, yes, but the gain from catching cancer early if it is there is enormous."

She also adds that women should do breast self-exams every month.

"If you feel anything different, bring it to your doctor's attention immediately," adds Dr. Ramshesh. "The goal is always to catch breast cancer early, when it's most treatable. And this is another thing in our control that we should do."