By Ian Ingram
— With some 250,000 participants, study rules out all but smallest risk increases
New research on a quarter-million women from four U.S. cohorts found no significant association between ovarian cancer and the use of powder-based products in the vaginal area.
Over a median follow-up of 11.2 years, incidence of ovarian cancer was 61 cases per 100,000 person-years among women who used powder in the genital area at any point compared with 55 cases per 100,000 for never users, a non-statistically significant difference (estimated HR 1.08, 95% CI 0.99-1.17), reported Katie O’Brien, PhD, of National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, and colleagues.
That translated to a risk difference of just 0.09% at age 70 (95% CI -0.02% to 0.19%), the researchers estimated.
Likewise, as described in JAMA, no significant difference was seen when comparing women considered frequent users (at least once a week) against never users (HR 1.09, 95% CI 0.97-1.23). Or for long-term users (at least 20 years) versus never users (HR 1.01, 95% CI 0.82-1.25).
“[T]his is, to our knowledge, the largest study of this topic to date, and it is believed that no other large prospective cohorts have collected data on powder exposure in the genital area,” O’Brien’s group wrote.
Since the 1976 ban of asbestos from cosmetic talc, the International Agency for Research on Cancer has called talc-based body powder a “possible” carcinogenic based on case-control studies and a meta-analysis that found an association between its use on or near the vagina (on underwear, sanitary napkins) and ovarian cancer.
“However, these findings may be affected by recall bias, and a recent surge in talc-related lawsuits and media coverage has increased this possibility,” O’Brien’s group wrote. “Thus, it is crucial to evaluate the talc-ovarian cancer association using prospective data.”
For their study, they pooled data from 81,869 women in the Nurses’ Health Study (enrollment 1976), 61,261 women from the Nurses’ Health Study II (enrollment 1989), 40,647 participants from the Sister Study (enrollment 2003-2009), and 73,267 participants in the Women’s Health Initiative Observational Study (enrollment 1993-1998). Median age at enrollment across the four cohorts was 57.
Ovarian cancer was diagnosed in 2,168 women across the studies, for an incidence of 58 cases per 100,000 person-years. Overall, 38% had reported using powder in the genital area, with long-term use in 10% and frequent use in 22%.
“One of the primary drivers of research on genital use of talc-based products and ovarian cancer has been the potential link between talc and asbestos, which can occur together in nature,” O’Brien’s group wrote. “In an analysis limited to the older cohorts in which women may have started using powder before the asbestos ban of 1976, the estimated effect remained consistent, with no association observed in the younger cohorts.”
Recent reports have suggested, however, that some talc-based products may have contained asbestos after this ban.
“The putative etiologic mechanism for talc as a causative agent in epithelial ovarian cancer is via uptake into the vagina, through the cervix and uterus, and through the fallopian tubes into the peritoneal cavity,” explained Dana Gossett, MD, MSCI, of University of California San Francisco, and Marcela del Carmen, MD, MPH, of Harvard University Medical School in Boston, in an accompanying editorial. “The evidence of talc in ovarian specimens lends credence to a transgenital transit mechanism.”
When the current analysis was restricted to women with patent reproductive tracts, an association between ever use of powder and ovarian cancer seemed to surface (HR 1.13, 95% CI 1.01-1.26), but tests for interaction between those with and without patent reproductive tracts lacked significance (P=0.15).
Other subgroup analyses — age, menopausal status, race, follow-up time, use of hormone therapy, body mass index, parity, hysterectomy, and tubal ligation — revealed no significant differences.
“[D]espite 3.8 million person-years of observation in the study population, the number of ovarian cancer cases was small, and it is possible that the study was underpowered to detect small increases or decreases in ovarian cancer rates,” Gossett and del Carmen wrote. “Future analyses would be strengthened by focusing on women with intact reproductive tracts, with particular attention to timing and duration of exposure to powder in the genital area.”
They pointed out that in women with patent reproductive tracts, frequent powder use appeared to increase the risk for ovarian cancer (HR 1.19, 95% CI 1.03-1.37, P=0.03 for trend), though no association was seen for long-term use.
Gossett and del Carmen cautioned that with the currently low rates (~25%) of powder use among women in the U.S., acquiring these data may not be attainable.
The study was supported by the Intramural Research Program of the National Institutes of Health; the National Institute of Environmental Health Sciences; the U.S. Department of Defense Ovarian Cancer Research Program; the National Heart, Lung, and Blood Institute; and the U.S. Department of Health and Human Services.
O’Brien reported no conflicts of interest. Co-authors disclosed relationships with Pfizer, AMAG, Mithra, Merck; and institutional support from Allergan, Myovant, and Endoceutics.
Gossett disclosed a relationship with Bayer related to the Mirena intrauterine device.
This article was published by Medpage Today.