Breast cancers that arise before age 40 tend to be more aggressive. But young women who undergo "breast-conserving" surgery are just as likely to survive as those who have a mastectomy, a preliminary study finds.

The study involved nearly 600 women under age 40 who were treated for breast cancer at one medical center. Some underwent a mastectomy, or removal of one or both breasts, while some had a lumpectomy, where only the tumor and some surrounding tissue are removed.

Over 5.5 years, 12% of the women died, and the type of surgery made no difference in their survival odds, the researchers found.

Experts said the findings reflect the fact that other factors are key in breast cancer outcomes, including the non-surgical treatments women receive. Women who undergo lumpectomy often receive radiation, too, for instance. And those with hormone-sensitive tumors—as most breast cancers are—typically receive years of hormonal therapy to cut the risk of a recurrence.

In fact, the study found, hormonal therapy had a substantial effect on women's survival.

None of that means less-extensive surgery is for everyone, said lead researcher Dr. Christine Pestana, a breast surgical oncology fellow at Levine Cancer Institute, part of Atrium Health in Charlotte, N.C.

Young women at high genetic risk of a recurrence, due to mutations in genes like BRCA1 and BRCA2, may want to opt for a double-mastectomy, Pestana said.

Even in the absence of gene mutations, she added, some women want that option—because it will ease their anxiety about a recurrence or may give them a better cosmetic result. For some women with smaller breasts, Pestana noted, mastectomy, possibly followed by breast reconstruction, might be preferable to a lumpectomy for those cosmetic reasons.

Dr. Mediget Teshome is a breast surgical oncologist at MD Anderson Cancer Center in Houston.

She said the findings add to evidence that when it comes to breast cancer survival, it's not the type of surgery that's important, but other factors—including the biology of a woman's particular cancer and the additional treatments she gets.

Teshome also agreed there is no one-size-fits-all surgery choice. Instead, she said, the decision is an individual and often "nuanced" one.

There are many things for a woman to consider and discuss with her doctors, according to Teshome: the specific characteristics of her breast cancer, her personal risk of a future recurrence, and the potential effects of surgery choice on her long-term quality of life, to name a few.

Pestana was scheduled to present the findings Friday at the annual meeting of the American Society of Breast Surgeons in Las Vegas. Studies released at meetings are generally considered preliminary until they are published in a peer-reviewed journal.

Most of the time, breast cancer is diagnosed after the age of 50. But while the rate is low among women younger than 40, it is on the rise, Pestana said, making it even more important to understand the impact of treatment choices on their long-term prognosis.

She pointed to the "Angelina Jolie effect," where the actor's revelation that she'd had a double-mastectomy to cut her breast cancer risk has influenced other young women to choose that option as a breast cancer treatment.

What's important to remember, Pestana said, is that Jolie carries a BRCA mutation that greatly increases the risk of breast cancer. For young women at average genetic risk, she said, evidence is lacking that a double-mastectomy improves survival over breast-conserving surgery.

The new findings are based on 591 women younger than 40 who were treated for breast cancer between 2010 and 2019. Most had earlier, stage 1 or 2 breast tumors, and none had cancer that had spread throughout the body.

Close to two-thirds of the patients underwent a mastectomy, Pestana said, while the rest had a lumpectomy.

The researchers found that once other factors were taken into account—including the stage and aggressiveness of the cancer, and other treatments women received—the choice of lumpectomy or mastectomy had no bearing on survival odds.

Another treatment did, however: Among women with hormone-sensitive cancer, those who did not receive hormonal therapy were three times more likely to die than those who did receive it.

Both Pestana and Teshome stressed the importance of "shared decision-making" between women and their care team—which means discussing the pros and cons of all treatments, as well as a woman's personal values.

Ultimately, Pestana said, "patients must be comfortable with their decision, and their doctors should support an informed choice."

--Amy Norton