Results from the largest reported investigation to date indicate there is no statistically significant association between use of powder in the genital area and the risk for ovarian cancer.
The study did not specify the use of talcum powder, although most powder products do include some mineral talc, the authors note.
This is a highly contentious issue, inasmuch as the potential link between talc and ovarian cancer has fueled high-profile litigation cases against Johnson & Johnson, as previously reported by Medscape Medical News.
The new findings come from a pooled analysis of data in four large US cohorts that was published online January 7 in JAMA.
In an accompanying editorial, Dana R. Gossett, MD, MSCI, of the University of California, San Francisco, and Marcela G. del Carmen, MD, MPH, of Harvard University Medical School in Boston, said these study findings may provide some reassurance.
"The overall conclusion [is] that there is no demonstrable statistically significant association between use of powder in the genital area and ovarian cancer risk," they write. "This is the key finding of the study."
However, the finding comes with several key caveats, according to both the study authors and outside experts who were approached for comment by Medscape Medical News.
All agreed that no definitive conclusions can be drawn.
The study may have been underpowered to detect small increases or decreases in ovarian cancer rates, the study authors acknowledge.
"Although this is the largest study ever done, our findings are not definitive," lead author Katie O'Brien, PhD, of the National Institute of Environmental Health Sciences at Research Triangle Park, North Carolina, told Medscape Medical News. "We cannot make any determinations about causation."
The findings do suggest a small increased risk for women with an intact reproductive tract, O'Brien noted.
However, the editorialists note that this finding (with a hazard ratio of 1.13) "is below the effect size that epidemiologists generally consider important and should not be selectively highlighted by the statistically unsophisticated reader as evidence of a relationship."
Patency of the reproductive tract remains a key factor in exposure, experts have pointed out. For a woman who has undergone a hysterectomy or tubal ligation, for instance, a carcinogen that comes into contact with the vulva or vagina could not reach the fallopian tubes and ovaries to cause the local inflammation thought to trigger carcinogenesis.
When approached for comment, Don S. Dizon, MD, professor of medicine at Brown University and director of women's cancers at Lifespan Cancer Institute in Providence, Rhode Island, emphasized that many factors can affect risk
"This is an example of the difficulties in concluding that any one factor increased the risk of ovarian cancer," Dizon told Medscape Medical News. "The risk is likely to be multifactorial, and there are far better data to support other factors that also determine risk," he said. As an example, he cited the protective effects of hormonal therapy and the value of genetic risk evaluation and testing for familial cancer predisposition syndromes.
Dizon noted that the study did show a significant association between the use of genital powder and ovarian cancer risk in the subgroup of women who had a patent reproductive tract.
However, Dizon said he remains unconvinced that there is an increased risk for ovarian cancer from the use of talc body powder in the genital area. Even so, he acknowledged that, "short of definitive proof, which would require a randomized controlled trial, the worry about the risk will always persist."
When discussing the "hows" and "whys" of an ovarian cancer diagnosis with patients and their families, Dizon said he does not include genital talc powder in the discussion of possible risk factors. He simply acknowledges the lack of conclusive evidence that genital use of talc is or is not associated with the risk for ovarian cancer. "I do think that if women are worried about exposures, simply not using these products make sense," he said.
For the study, the researchers created a cohort of more than 252,745 women using prospective observational data pooled from the Nurses' Health Study II (NHS II), the Sister Study (SIS), and the Women's Health Initiative Observational Study (WHI-OS).
The NHS, the WHI-OS, and the SIS previously reported associations between genital use of powder and ovarian cancer risk. The current pooled analysis included updated data from additional cases and longer follow-up, the researchers note.
With a median patient age at baseline of 57 years and a median follow-up of 11.2 years, the analysis showed that 2168 women developed ovarian cancer. Among ever-users of genital powder, the incidence of ovarian cancer was 61 cases/100,000 person-years; among never-users, the incidence was 55 cases/100,000 person-years (hazard ratio [HR], 1.08; 95% confidence interval [CI], 0.99 – 1.17). By age 70 years, the estimated difference in ovarian cancer risk between powder users and nonusers was 0.09%.
Analyses across subgroups of women that compared those who had an in situ uterus and fallopian tubes with those who had a nonpatent reproductive tract showed that tests for heterogeneity were not statistically significant for any comparisons (HR, 1.13, vs HR, 0.99; P = .15). When frequent users and never-users with a patent reproductive tract were compared, the analysis showed that the HR was 1.19 (95% CI, 1.03 – 1.37; P for trend = .03).
The editorialists agree that the study may have been underpowered to detect small increases or decreases in ovarian cancer rates. They also point out that the cohort studies from which the data were taken "may have lacked the power to detect a true association given the relative rarity of epithelial ovarian cancer."
Given the the small number of ovarian cancer cases in a study population with 3.8 million person-years of observation, the editorialists suggest that in future, "analyses would be strengthened by focusing on women with intact reproductive tracts."
Attention should be paid to the timing and duration of genital powder exposure, they add, but they also note that with the present low rates of genital powder use among US women, collecting sufficient data may not be feasible.
Risk for Women With Greatest Exposure
Another expert who was approached for comment, Daniel W. Cramer, MD, ScD, professor of obstetrics, gynecology, and reproductive biology at Brigham and Women's Hospital, Harvard Medical School, commented: "This study is by no means the final word on the talc story.
"For those who would say that the overall association is too weak to be of public health importance, this study can say nothing about women who had daily talc use for more than 20 years," Cramer told Medscape Medical News. "I have argued this is the group of women who are at greatest risk for ovarian cancer from this level of exposure."
Cramer, who has studied the topic for more than 3 decades and has acted as an expert witness for the prosecution in litigation proceedings, advises women not to use talc for genital hygiene.
The current analysis "does not shed any entirely new light on the topic," he said. The findings must be taken in context with case-control studies that provide substantial data for a stronger association and a dose-response than cohort studies.
It is already known that the cohort studies find a weaker association between genital talc use and ovarian cancer, Cramer said. Exposure measures that combine both frequency and duration of use are not available in these studies.
Physicians have likely formed an opinion on this topic already, and this study may do little to change their minds, he pointed out. "At least I hope that physicians will not suddenly conclude that an elevated hazards ratio can be ignored simply because the hazard ratio did not reach the somewhat arbitrary bar of 5% but may have said, 'Yes, the association is real' if the HR were 1.08."
Cramer noted that in a 2014 editorial entitled "Talc Use and Ovarian Cancer:Between a Rock and a Hard Place," one of the current study authors suggests it was unlikely that new conventional epidemiologic studies would be able to settle the issue of causality.
This could soon change, Cramer predicted, noting that "there is some emerging laboratory data that I believe can move the bar."
The study was funded by the Intramural Research Program of National Institutes of Health, the National Institute of Environmental Health Sciences, the Intramural Research Program of the National Cancer Institute, the US Department of Defense, the National Heart, Lung, and Blood Institute, and the US Department of Health and Human Services. O'Brien has disclosed no relevant financial relationships. Several coauthors of the study have reported relationships with industry. Gossett has reported a relationship with Bayer. Del Carmen has disclosed no relevant financial relationships. Cramer has acted as an expert witness on behalf of users of products that contain talc. Dizon has disclosed no relevant financial relationships.
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Cite this: Largest Study So Far on Genital Powder and Ovarian Cancer - Medscape - Jan 07, 2020.