NIEHS researchers found a positive association between douching and ovarian cancer, but no association between genital talc use and ovarian cancer. Published online June 20 in the journal Epidemiology, the research used data from women participating in the Sister Study, which examines environmental and genetic risk factors for breast cancer and other diseases in sisters of women who have had breast cancer.
According to the paper’s corresponding author, Clarice Weinberg, Ph.D., deputy head of the NIEHS Biostatistics and Computational Biology Branch, 154 of the 50,884 women enrolled in the Sister Study developed ovarian cancer during approximately six years of follow-up. Although the number of ovarian cancer cases was relatively small, Weinberg said sisters in the study were more likely to develop ovarian cancer due to their family history of breast cancer.
"A woman who has a sister with breast cancer has twice the risk of getting breast cancer, but also as much as a 60 percent increase in her risk of developing ovarian cancer," Weinberg said. "The Sister Study gives us more statistical power to examine an otherwise rare cancer like ovarian cancer."
First paper to examine douching and ovarian cancer
Before this paper, a number of studies had examined the association between genital talc use and ovarian cancer, but none had investigated a link between douching and ovarian cancer. To determine if talc use and douching were involved in the development of ovarian cancer, Sister Study participants were asked about reproductive and health history, lifestyle, and use of personal care products. In the cohort as a whole, women who used talc were twice as likely to douche as women who did not use talc, raising the possibility that the correlated behavior of douching might explain some of the earlier talc findings.
In the Sister Study, women who douched were nearly twice as likely to develop ovarian cancer as women who did not, regardless of whether they also used talc. Possible explanations for the association include that douching forces toxins into the reproductive tract or that some douching solutions or douching devices contain phthalates. Levels of phthalates have been reported to be higher among women who douche.
Study design makes a difference
Katie O’Brien, Ph.D., a postdoctoral fellow in Weinberg’s branch, directed the research, supervising an undergraduate summer student who wrote the manuscript (see sidebar). O’Brien said although most of the research papers on the topic found a positive association between talc and ovarian cancer, most of them were from case-control studies, in which women with ovarian cancer were asked about their exposures after they were diagnosed.
According to O’Brien, being diagnosed with the disease could change women’s behaviors or their recall of talc use. The Sister Study is a prospective cohort study, meaning researchers asked participants about exposures to talc before they were diagnosed.
"This paper is the third cohort study to show no association between talc use and ovarian cancer, so we need to figure out what could be responsible for the difference," O’Brien said.
As lead researcher for the Sister Study, NIEHS Epidemiology Branch Chief Dale Sandler, Ph.D., served as co-senior author on the paper. Sandler said the role of genital talc use in ovarian cancer has been a longstanding and contentious issue. She explained that the topic was difficult to study because women may have used powders that do not contain talc, and comprehensive product use histories are difficult to collect. Nevertheless, she believes prospective studies like this one may eventually lead to a definitive answer.
"By combining data from multiple cohorts, epidemiologists may be able to tackle this issue more thoroughly," Sandler said.
Citation: Gonzalez NL, O’Brien KM, D’Aloisio AA, Sandler DP. Weinberg CR. 2016. Douching, talc use, and risk of ovarian cancer. Epidemiology; doi:10.1097/EDE.0000000000000528 [Online 20 June 2016].