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Gut Check looks at health claims made by studies, newsmakers, or conventional wisdom. We ask: Should you believe this?

The claim:

Swayed by the power of celebrity, many women needlessly rushed to get genetic testing for the cancer-causing BRCA mutations right after actress Angelina Jolie announced in May 2013 that she underwent a double mastectomy based on a positive BRCA test, concluded a study in the BMJ last month.

Tell me more:

Other studies, too, have reported an uptick in BRCA testing after Jolie’s announcement — the “Angelina effect” — but this one went further. Although insurance claims for nearly 10 million women aged 18 to 64 showed that BRCA testing rose 64 percent in the 15 days after Jolie described her BRCA result and surgery, that wasn’t followed by additional mastectomies.

One would expect an uptick in BRCA testing to be followed by an uptick in mastectomies, reasoned health economist Dr. Anupam Jena and graduate student Sunita Desai of Harvard Medical School: When women learn they carry a cancer-causing BRCA mutation, more undergo mastectomy than if they had remained in the dark. But the rate of mastectomy within 60 days of a BRCA test fell, they found, from 10 percent of tested women in the four months before Jolie’s announcement to 7 percent in the eight months after (through the end of 2013). That suggests most women who underwent BRCA testing because of Jolie’s announcement had a lower probability of a BRCA mutation than women tested before her announcement, the researchers concluded.

BRCA testing is recommended for women with a family history of breast or ovarian cancer or other risk factors, but the authors said their finding suggests that most of the women who got tested didn’t have an elevated risk of cancer and provides a cautionary tale about the unintended consequences of celebrity endorsements of medical tests and procedures. They calculated that the extra testing cost as much as $13.5 million.

Read more: As revenue falls, a pioneer of cancer gene testing slams rivals with overblown claims

Really?

Genetic counselors, physicians, and BRCA-positive women have lit up social media attacking the study.

For one thing, the conclusion that a large majority of the Angelina-effect women tested negative (and should never have undergone testing in the first place) is an inference based on the lower rates of mastectomy. The researchers “do not know how many of these women tested positive” for a cancer-causing mutation, Mary Freivogel, a genetic counselor in Denver and president-elect of the National Society of Genetic Counselors, told STAT. It’s therefore quite a leap to infer that BRCA testing was unnecessary.

Critics have also argued that 60 days is too short a period to count the number of mastectomies resulting from BRCA tests.

Writer Suzanne Zuppello was found to have a cancer-causing BRCA1 mutation in March 2015; she had a double mastectomy that October. That lag isn’t unusual. It takes two weeks to get test results, at least a week to see a breast surgeon and gynecologic oncologist, weeks to decide between surveillance (frequent breast imaging) and surgery (both of which are equally valid options for BRCA-positive women), weeks to schedule the required pre-mastectomy mammogram or MRI, time to think long and hard about surgery, and at least a week to get on a surgeon’s schedule, Zuppello wrote in Medium. All that mitigates against a quick post-BRCA mastectomy.

Another odd thing about concluding that “Angelina effect” women weren’t in the high-risk group for whom BRCA testing is recommended is that it’s not easy to get insurers to cover the $3,000 test. They almost never do unless a woman has a strong family history of breast or ovarian cancer (as Jolie did). Since the Harvard researchers analyzed insurance claims, experts said, the test was probably covered because the women were suitable candidates for it — not women who were blindly, or in a panic, emulating a celeb.

“We do not know how many met standard guidelines for BRCA testing,” said Freivogel, but the insurance claims “tell me that most of these women probably did meet criteria for testing.”

Moreover, many women who learn they have a BRCA mutation opt for surveillance instead of mastectomy, in part because they fear undergoing such life-changing surgery. Women tested before Jolie’s announcement might have differed in a key way from those tested before: They might well have met the family history or other criteria for testing, but have been afraid to have it until Jolie’s brave announcement. That same fear and tendency to postpone life-changing decisions could account for why 10 percent of women tested before Jolie’s announcement had mastectomies within 60 days of their test compared to only 7 percent of those tested after.

Harvard’s Jena said his critics “are exactly right: 60 days may very well be too short for many women.” Although the drop in mastectomies within 60 days of BRCA testing was their main finding, he added, mastectomy rates within 90 and 180 days were also lower after Jolie’s announcement than before. Since the likelihood of mastectomy within 180 days “is quite high,” Jena said, “the vast majority of women who underwent BRCA testing as a result of Jolie’s editorial did not end up receiving preventive mastectomy, most likely because the additional tests obtained were negative.”

The verdict:

That’s a long chain of inference — no mastectomy within six months of BRCA testing implies no mastectomy, period; no mastectomy implies a negative BRCA result; a negative BRCA result implies the woman shouldn’t have undergone testing — and it makes for a shaky conclusion.