Backstory
There have been a number of high publicity lawsuits recently against Johnson & Johnson (J&J), with plaintiffs’ attorneys arguing that the corporation’s talc-based baby powder contained high enough traces of asbestos to cause their clients to develop cancer. In a number of the cases to date (there are more than 16 thousand of these cases awaiting trial) the juries have voted in favor of the plaintiffs, maintaining that J&J should be held responsible because they did not warn consumers of the risks involved with using the baby powder.
But those are juries in real world legal cases. In the scientific world, the issue is far less clear cut and the jury is definitely still out. More specifically, there have been only a small number of studies to demonstrate a statistically significant link between talc and ovarian cancer, with the majority of studies on the topic either finding a weak (statistically insignificant) to modest correlation between cancer and talc or in a small number of studies, no link at all.
A primary reason for the lack of continuity in the findings on this topic is that ovarian cancer is relatively rare, so there are only a small number of subjects to investigate. With only a small number of subjects with ovarian cancer participating in the studies, the pool is not large enough to statistically detect the potential for small changes in risk from baby powder use. Secondly, the majority of studies on the topic have asked women to remember back–sometimes many years–about their hygiene practices involving the use of talc in the genital area. As human memory–especially from a long time ago–can be notoriously bad, the results from many of these studies may potentially be tainted with recall bias and therefore seen as unreliable.
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Enter a new, large-scale examination on the link between talc and ovarian cancer
In the largest study to date to explore the possible link between talc use and ovarian cancer, researchers from the U.S. National Institute of Environmental Health Sciences (NIEHS) examined the results of four previous government studies on the topic. The new cohort study involved examining the responses of 252,745 female participants who had previously been asked about whether they had ever used powder on their genitals. Approximately 40 percent of the female study participants said they used baby powder.
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The results
The new study failed to find a significantly increased risk of ovarian cancer from talc use overall. (Overall, women who had used talc for feminine hygiene sometime during their lifetimes had an 8 percent increased risk of developing ovarian cancer compared with those who were not exposed to talc. That difference was not deemed to be statistically significant.)
However an increased risk for ovarian cancer did appear among certain women who used talc on the genital area. That increased risk was for women with intact reproductive tracts* (that is, women who never had a hysterectomy and who never had their fallopian tubes surgically tied off).
Among this group, an increased risk for cancer among powder users was statistically significant. The data demonstrated that women with an intact reproductive tract who reported using baby powder had a 13 percent higher risk of developing ovarian cancer compared to women who never used the product. That risk rose to 19 percent among those women who used baby powder at least once a week.**
A total of 2,168 participants in the studies examined developed ovarian cancer, which has a lifetime risk of approximately 1.3 percent.
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*The prevailing theory of how talc powder could cause ovarian cancer: When the powder is applied to the genital area, asbestos-tainted talc travels up the vagina, through the cervix, uterus and fallopian tubes, where it comes into contact with the ovaries, potentially causing inflammation that can lead to cancer.
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**These results come with an important caveat: the percentage of increased risk for cancer for this group are below the size that many epidemiologists consider important or noteworthy.
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So did the new study demonstrate a clear link between talc use and cancer?
According to the lead researcher on the project, overall, not really.
“We got an ambiguous answer. This was the largest study ever done, but because ovarian cancer is such a rare disease, it was still not big enough to detect a very small change in risk [from talc use].”
-Dr. Katie O’Brien, NIEHS epidemiologist and lead researcher
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Conclusion
When all is said and done, the number of study participants with diagnosed ovarian cancer was too small to draw definitive conclusions about the overall risk levels of talc. As statistical expert Dr. Kevin McConway, Emeritus Professor of Applied Statistics put it:
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“One thing this research clearly demonstrates is how difficult it is to tie down whether something like this is indeed a risk factor for cancer. Despite this being a good, competent, careful study involving over quarter of a million women, it still leaves room for doubt about the association, if there is one, between using powder in the genital area and ovarian cancer. There is still uncertainty about whether any such association exists. If it does exist, there is uncertainty about whether the powder itself is what causes any increase in cancer risk. And there’s also uncertainty about what the size of the risk increase is, if it there is one. But what the research does establish, I’d say, is that if using talc or other powder on that part of a woman’s body does really increase the risk of ovarian cancer, the increase in risk is likely to be small…
“…even if a finding is statistically significant, that doesn’t mean that it’s definitely real – there is still some uncertainty involved. Importantly, the researchers compared the risk difference in women who had a patent reproductive tract, with the risk difference in women who didn’t, and found that it remains statistically plausible that those two differences are actually equal, despite the fact that one is statistically significant and the other is not. Putting it crudely, there’s too much statistical variability, because of the relatively small number of cancer cases, to come to any very clear conclusions on which effects might be real and which not.” (source)
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Whether or not these latest findings will influence future juries remains to be seen.
Journal Reference: Katie M. O’Brien et al. ‘Association of Powder Use in the Genital Area With Risk of Ovarian Cancer’ by was published in JAMA, January 7, 2020. DOI:10.1001/jama.2019.20079
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