Removing both breasts to treat cancer affecting only one side doesn't boost survival chances for most women, compared with surgery that removes just the tumor, a large study suggests. The results raise concerns about riskier, potentially unnecessary operations that increasing numbers of women are choosing.

The study involved nearly 200,000 California women treated for cancer in one breast and followed for several years afterward.

Ten-year survival rates were nearly identical — roughly 82 percent — for women who had lumpectomies to remove the tumor plus radiation, and for those who had double mastectomies. Women who had a single mastectomy, removal of just the cancerous breast, fared slightly worse.

The results confirm what many doctors have suspected, said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society.

"There's no guarantee that by having the second breast removed that you will do better," said Lichtenfeld, who had no role in the research.

In the study, just over half the women had lumpectomy treatment. But the number who had double mastectomies increased substantially to 12 percent between 1998 and 2011. The trend was most notable in women younger than 40, climbing from just 4 percent to 33 percent.

Other research suggests that removing both breasts to treat one-sided cancer may improve survival chances for the relatively small number of women who have genetic breast cancer or strong family histories of the disease, said study co-author Scarlett Gomez, a research scientist with the Cancer Prevention Institute of California. But most breast cancer patients have neither of those risks.

The medical community is paying increasing attention to overtreatment and excessive costs, and the study results raise questions about reasons for rising use of an expensive, potentially risky treatment "of dubious effectiveness," the researchers said.

Patients' preferences and fear that cancer will return play a role, but that fear "usually exceeds estimated risk," the study said.

Reasons why survival was slightly worse for woman who had just one breast removed are uncertain, although this treatment is more common among Hispanic and Black women and those with lower incomes and public insurance than among wealthy whites.

The study was published Tuesday in this week's Journal of the American Medical Association. A journal editorial notes that the study echoes previous research and adds to a debate about the rising prevalence of double mastectomies.

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(Photo: WILL & DENI MCINTYRE)