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When it comes to diagnosing and treating breast cancer, enormous strides have been made in the past two decades. Earlier detection plus better therapies and gene-typing of cancers allow much more directed and effective therapies. As a result, breast cancer deaths have been slashed by 30 percent. But there’s still a lot of misinformation out there about how to control your risk.

For example, there are claims bouncing around the Internet that wearing a bra can lead to breast cancer. Nope! A definitive new study of 1,044 women with breast cancer found no link between use of a bra and their cancer risk. The type of bra, when they started wearing a bra and how many hours a day they wore one didn’t matter either.

So if you’re one of the almost 300,000 North American women who will be diagnosed with breast cancer this year, here are the latest facts that actually might save your life.

FACT: WOMEN OVER 40 DO NEED MAMMOGRAMS

We’ve read headline-grabbing studies suggesting that mammograms aren’t worth it before age 50. But we agree with groups such as the American Cancer Society and the National Comprehensive Cancer Network that believe yearly screening should begin at age 40. (Younger if you’re at high risk.) Some research shows this check can cut cancer deaths by 15 percent in 40-something women.

Bottom line: Don’t opt out if you’re in your 40s (one in five women with breast cancer is younger than 50). And make sure to get regular mammograms in your 50s and beyond. Women of all ages also need regular clinical breast exams, performed by their health-care provider. Self-checks are smart, too. Up to 40 percent of cancers are discovered by women themselves.

FACT: CANCER-PREVENTING TAMOXIFEN NEEDS DARK NIGHTS

If you have hormone-receptor-positive breast cancer and take tamoxifen, a selective estrogen response modifier, you know that this drug can cut your relative risk for repeat breast cancer by as much as 50 percent. Now, a Tulane University lab study suggests that your sleep environment might impact this medication’s effectiveness. Seems even dim light at night reduces your body’s melatonin levels, making breast cancer cells resistant to tamoxifen.

Bottom line: The researchers suggest taking tamoxifen an hour or so before bedtime to take advantage of the natural increase in melatonin at night. Also, wear an eye mask or only have red-wavelength light in your bedroom and bathroom to block out blue-wavelength light during sleep.

FACT: KNOW YOUR RISK

We salute Angelina Jolie for going public with news that she carries the BRCA-1 gene mutation, which boosts breast-cancer risk — by 87 percent, in her case. She then chose to have both breasts removed to protect herself from her enormous genetic risk.

About 15 percent of women who get breast cancer have a family history, and one in 300-500 women in the general population carries one of the breast-cancer genes, BRCA-1 or BRCA-2 (rates are higher in some groups, such as Ashkenazi Jews).

Look at your family tree for warning signs: Did anyone have cancer before age 50, breast cancer in both breasts, ovarian cancer or male breast cancer? Knowing the answers can help you and your doctor decide if you would benefit from genetic testing.

Bottom line: Determine if you have a familial risk. But remember: 85 percent of breast cancers are not caused by an inherited gene. That’s why regular mammograms are so important!

FACT: YOU MAY NOT NEED A DOUBLE MASTECTOMY

In many situations, removing a healthy breast might not be necessary. A new Cancer Prevention Institute of California study found that for many women with early-stage breast cancer in one breast, removing both might not be the smart move. Less-invasive treatments turn out to produce the same survival rates, and risk for cancer in the healthy breast is low.

Bottom line: If you have cancer in one breast and are thinking about a double mastectomy, talk with your doctor so you can weigh your risks and benefits.

Mehmet Oz, M.D. is host of “The Dr. Oz Show,” and Mike Roizen, M.D. is Chief Wellness Officer and Chair of Wellness Institute at Cleveland Clinic. Consult with your physician before making changes to your personal regimen. To live your healthiest, tune into “The Dr. Oz Show” or visit sharecare.com