One in three breast cancer patients under 45 removed the healthy breast along with the breast affected by cancer in 2012, a sharp increase from the one in 10 younger women with breast cancer who had double mastectomies eight years earlier, a new study reports. The rate is especially high in some parts of the country, the study in JAMA Surgery found. Nearly half of younger women in five neighboring states — Nebraska, Missouri, Colorado, Iowa and South Dakota — had double mastectomies in 2010-12. Women often remove the healthy breast so they don’t have to worry about developing another cancer, even though there is no evidence that removing the healthy breast extends lives. Both the American Board of Internal Medicine and the American Society of Breast Surgeons recommend against the practice, called contralateral prophylactic mastectomy, unless a woman is at unusually high risk for a new cancer because of a condition like increased genetic risk, such as a mutation in the BRCA1 or BRCA2 genes. “This study again underscores the fact that women are making this decision out of anxiety rather than medical necessity,” said Dr. E. Shelley Hwang, the chief of breast surgery at Duke Cancer Institute, who was not involved in the study but has studied patients’ quality of life after double mastectomies.There was a large geographic variation in rates of double mastectomies across the country, which suggests that doctors aren’t properly explaining the risks and the lack of survival benefit to patients, Dr. Hwang said. “There are important regional differences in how communication occurs between patient and surgeons,” she said, noting “it is clearly not plausible that there are biologically based regional differences.” The new study looked back at 1.2 million women age 20 and older from 45 states and the District of Columbia who had been given an early stage breast cancer diagnosis in one breast between Jan. 1, 2004, and the end of 2012. (The only states not included, for various reasons, were Maryland, Illinois, Vermont, Kansas and Minnesota.) Most of the cancers were in women over 45. The data was compiled by the North American Association of Central Cancer Registries, and the investigators were from the American Cancer Society, Emory University, Dana-Farber Cancer Institute and Brigham and Women’s Hospital.Among women of all ages who had been given a diagnosis of breast cancer during this period, most — 58.4 percent – had lumpectomies to remove tumors from the affected breast, but left the healthy breast alone. Another 32.9 percent had a single mastectomy, and 8.7 percent had both breasts removed, the study found. But the percentage of women of all ages who chose to have both breasts removed increased to 13 percent of all those who had surgery in 2012, up from 4.5 percent in 2004. The rate of double mastectomies was highest among women under 45. But the rate increased among women 45 and older as well. The percentage of older women having double mastectomies rose to 10.4 percent in 2012, up from 3.6 percent in 2004. The lowest rates of double mastectomies for younger women over all were in Hawaii, where 15.7 percent of all women with cancer in one breast had both breasts removed, and the District of Columbia, with a rate of 14.6 percent. The increasing rates and the regional variations across the country surprised the authors of the study, said Dr. Ahmedin Jemal, the senior author of the paper, who is vice president of surveillance and health services research at the American Cancer Society. “There might be differences in culture, there might be differences in provider recommendations,” he said, adding that studies suggest that women are less likely to opt for a double mastectomy when they are informed and the decision is driven by the physician. But he noted that the health care system reimburses physicians based on the number of procedures they do, and surgeons are paid more for a double mastectomy than a single mastectomy. Researchers initially thought that women would be more likely to choose a double mastectomy in regions where reconstructive surgery is more commonly done because they wanted symmetrical reconstructed breasts, but many states with high rates of double mastectomies do not have high rates of reconstructive surgery, and vice versa. Dr. Lisa A. Newman, the director of the breast oncology program for the Detroit-based multi-hospital Henry Ford Cancer Institute, wrote in a commentary accompanying the study that surgeons have “an ethical and moral imperative” to ensure that patients have accurate information and that treatments “prioritize optimal oncologic outcomes.” Though they should respect patient choice and “avoid being paternalistic,” she said, they should also make sure patients don’t panic and make impulsive decisions after finding out they have cancer. The breast cancer that is most likely to kill a patient is the first breast cancer because it is most likely to be discovered at a later stage and thus more likely to have spread, Dr. Newman said. The risk of a second unrelated cancer occurring in the healthy breast is small, and since a patient with a cancer history will be monitored closely “it will usually be detected early,” she said.