The number of women choosing to undergo a double mastectomy after a breast cancer diagnosis is on the rise, new research reveals. But a second study also finds that women who choose to have both breasts removed survive about as long as patients who choose less-invasive lumpectomy surgery instead.

In a third study released Tuesday, Canadian researchers report an "Angelina effect" that followed Angelina Jolie's announcement  in May 2013 that she had undergone a preventive double mastectomy.

The Hollywood actress chose the surgery after learning she had a defective BCRA1 gene, which significantly raised her risk of developing breast cancer.

Researchers from Sunnybrook’s Odette Cancer Centre in Toronto report there was a 90 per cent increase in the number of women referred for breast cancer genetic screening at a large screening facility in Toronto in the six months before and after Jolie's announcement.

While studies have shown that women with BRCA gene mutations can lower their risk for breast cancer with a double mastectomy, it's been less clear whether choosing the surgery helps to prolong survival for women already diagnosed with breast cancer.

In two studies published in JAMA, researchers at the Stanford University School of Medicine and the Cancer Prevention Institute of California looked at nearly 190,000 California patients diagnosed with cancer in one breast between 1998 and 2011 to see which treatment options they chose and how they fared.

Among the women, the majority (55 per cent) received a lumpectomy to remove only the cancerous tissue within the breast, followed by radiation treatments. Another 38.8 per cent received a unilateral mastectomy, meaning the entire affected breast was removed, while 6.2 per cent received a double mastectomy.

The difference in the long-term survival rates between the women who underwent the double mastectomies and those who received a lumpectomy followed by radiation treatment was "not statistically significant," the study found.

Dr. Allison Kurian, an assistant professor of health research and policy at Stanford, says the study helps to answer the question of whether the average breast cancer patient fares better with a double mastectomy or a lumpectomy.

She notes that a double mastectomy is a major procedure that involves significant recovery time and often a breast reconstruction procedure. A lumpectomy, on the other hand, is much less invasive.

Having a clearer understanding of which treatment offers a better hope for survival is important for both patients and their doctors, the authors say.

The study did find a slightly lower survival rate among women who underwent a unilateral mastectomy, compared to the other groups.

The researchers say this may be due to the fact that women who underwent a single mastectomy tended to also have a lower socioeconomic status than other patient groups. They also tended to be members of racial or ethnic minorities. The researchers say these patients may have been more likely to have other health problems, such as diabetes, that could have affected their cancer treatment.

In a second paper, the researchers also found that the rates of women choosing a double mastectomy have been growing substantially.

Using data from the California Cancer Registry, which covers nearly all women diagnosed with breast cancer in the state, the researchers found the percentage of breast cancer patients choosing double mastectomy increased from just 2 per cent in 1998, to 12.3 per cent in 2011, for an annual increase of 14.3 per cent.

Among women younger than 40, rates are rising even faster. The number of women in this age group choosing double mastectomies is increasing by 17.6 per cent annually, from 3.6 per cent in 1998 to 33.0 per cent in 2011.

The researchers note that non-Hispanic white women were more likely to choose a double mastectomy, as were those with private insurance.

The authors say that with growing concerns that patients are being "overtreated," it's important for both patients and their doctors to weigh the risks and costs of double mastectomies against any benefits.