CHICAGO — 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.