Aspirin & breast cancer: another case study in communicating observational studies

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There’s undoubtedly going to be a lot of miscommunication about the latest analysis coming out of the Nurses Health Study, which looks at the impact of different lifestyle factors on women’s health.

This time they tracked aspirin use, and then saw how many women were diagnosed with breast cancer. That’s an observational study – not a trial – and it can’t prove cause and effect.

The analysis showed that women who regularly took aspirin had fewer diagnoses of breast cancer.

What you can say is that this was a strong statistical association in a big study. But you can’t say it established a benefit because such a study can’t prove cause-and- effect.

Now here comes the NBC Nightly News – from Vancouver for the Olympics – with the water and the mountains in the background. And, rather than a carefully scripted videotape piece, we get live chatter between anchor Brian Willams and NBC chief medical editor Dr. Nancy Snyderman. Excerpts:

Brian Williams: “What is the benefit shown here?”

Snyderman should have stopped him right there. Benefit? As we’ve said, you can’t establish benefits from a study that can’t prove cause-and-effect. Sorry, but the language is important. See our primer on this topic.

In her answer, Snyderman briefly said, “They didn’t look at cause-and-effect…” but that’s awkward. It takes seconds to say, “They followed women who took aspirin and then saw how many got breast cancer. That doesn’t prove anything, but it does show a strong statistical link that will lead to more study in this area.” This is one of the pitfalls of trying to explain research in a live shot. She had a lot to say and she was live. She didn’t quite get there.

Williams continued: “That sounds almost anecdotal. What do we really know?”

Snyderman: “Well it’s not anecdotal but it is observational.”

Huh? Again, I know she tried, but that’s just jargon to viewers watching her with the water and the mountains in the background. She never explained what observational meant, or what the limitations of an observational study are.

Snyderman: “So here’s what I think you can say. There’s no proof that taking aspirin prevents breast cancer. But if you’ve been diagnosed and you’re on aspirin for another reason, it may be one extra benefit and, frankly, a reason to sleep a little better at night. ..So right now if you’re on aspirin, and you’re tolerating it and you’ve had a diagnosis of breast cancer, this is good news.”

Look at the cumulative language of this NBC story: “no proof that taking aspirin prevents breast cancer” but then again “benefit…reason to sleep a little better at night…this is good news.”

I don’t think you can say that at this point after an observational study.

Again, maybe this is one that should have been carefully scripted and pre-taped – rather than another NBC piece trying to capitalize on the beauty of Vancouver in the background for a live shot.

[2017 Update: This NBC video is no longer available]

For a better example of how to handle such a story, look at how Liz Szabo covered the caveats in her USA Today story:

“A study in August also found that aspirin offered a potential benefit against colon cancer.

Yet neither study proves that aspirin keeps cancers in check, Holmes says. That’s because doctors in each study merely followed patients for several years, noting which patients developed cancer and, of those, which took aspirin. So it’s possible that something other than aspirin controlled their tumors, Holmes says.

For proof, doctors would need to conduct a “gold standard” trial in which doctors randomly assign one group of patients to take a aspirin, then compare their progress with patients randomly assigned to a placebo, says Eric Jacobs, a scientist at the American Cancer Society.”

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Comments (12)

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Ken Leebow

February 17, 2010 at 11:00 am

I did see this live and thanks to being a loyal reader of your website and blog dismissed the entire story.
Thanks for your work and efforts.
Ken Leebow
PS. As it relates to health, diet, and lifestyle, I read hundreds of emails and stories. So many contradict one another.

Andrew Holtz

February 17, 2010 at 1:22 pm

Tara Parker-Pope put it nicely in a recent NY Times piece on Vitamin D:
“And since most of the data on vitamin D comes from observational research, it may be that high doses of the nutrient don’t really make people healthier, but that healthy people simply do the sorts of things that happen to raise vitamin D.”
It takes just 10 seconds to read that line.
Her story then went on to quote a researcher listing some of the plausible ways (outdoor exercise, better diet) that people might be improving their health and coincidentally boosting their vitamin D levels. Any story about the results of an observational study should include similar plain-English context.
Parker-Pope also wrote:
“Although consumers may be tempted to rush out and start taking 2,000 I.U.’s of vitamin D a day, doctors warn against it. Several recent studies of nutrients, including vitamins E and B, selenium and beta carotene, have proved disappointing — even suggesting that high doses do more harm than good, increasing risk for heart problems, diabetes and cancer, depending on the supplement.”
It’s actually quite easy to include the proper perspective in these sorts of stories… using simple language and plain facts. Shame on journalists who don’t try.

February 18, 2010 at 9:51 pm

I analyzed the embarrassing gushing in US News by Dr. Bernadine Healy on this story, who of all people, should know better. As a doctor myself, I try to reserve judgement (although I have been known to get swept up in media hype every now and then, though not for very long, I like to think!)
You know I have a lot of respect for her as a doc, but I would tend to agree with you that the full judgement should be reserved for the prospective study.
Also, I am under the understanding that aspirin and breast cancer recurrence has been analyzed in other studies and not shown to associate with improved outcomes. Even though the new study was large, it may not be consistent with previous research.
Another great post, thanks for this.

Alison Dean

February 19, 2010 at 12:24 am

My thanks to Mr. Holtz for helping clarify an emotional topic. Currently undergoing treatment for breast cancer, I was initially tempted to add aspirin to my daily regimen as soon as I saw the news-feed, as in ‘can’t hurt, might help.’ But I’m glad to be reminded of the nature of spurious correlations, and reminded that before I became a cancer statistic I was a trained scientist. I’ll certainly be looking to participate in the research, though.

Elaine Schattner, M.D.

February 19, 2010 at 2:00 pm

I agree that the effect of aspirin use is not necessarily causative and should not be assumed to be so.
Nonetheless, as studies in oncology go, these findings are huge – powered by a large sample size, evaluation in many humans, extreme (stunning!) differences in outcome among the different albeit self-reported “treatment” groups, and solid statistical analysis of the findings. Many non-randomized, pharma-sponsored and otherwise imperfect chemo trials are published with much fanfare but small benefit – like reduction in recurrence from breast cancer death by 10 or 15 percent.
I think the impact and potential significance of these findings were under-emphasized in the media, overall, because aspirin is an unexciting, old drug.

Chrs Flowers

March 8, 2010 at 11:34 am

Another thought here is that patients who take aspirin also take their hormone treatment (tamoxifen or aromatase inhibitor).
Prior studies show that many patients drop their hormone therapy a few years out from their initial breast cancer treatment. If they are compliant with aspirin, maybe they also take their tamoxifen?