Can talcum powder cause cancer?
Talcum powder is an unlikely candidate for world news headlines - but that's exactly what has happened this week, after Johnson and Johnson was ordered to pay an American woman who developed ovarian cancer more than £40 million in compensation. The company plans to appeal, and claims there is no evidence that their product causes cancer - but controversy still rages.
The trouble it, it's very difficult to prove either way - and as I discussed in a recent blog, it's all down to teasing out the difference between 'association' and 'causal link'.
When a possibility of a link between two things is raised, scientists set to work devising studies to prove or disprove the connection. At an early stage, they usually use laboratory studies in human cells and in animals. The studies in animals exposed to talcum powder have shown conflicting results as far as cancer is concerned. In some studies, animals exposed to talc developed more tumours than similar animals who weren't exposed, while in others there was no difference between the groups in terms of cancer development.
In humans, it's far harder to work out cause and effect. Before medicines are approved, they have to go through a whole series of tests - and the 'gold standard' is the RCT, or randomised controlled trial. In an RCT, subjects are divided into two groups - one group is given the drug being studied, and the other is given a 'placebo' (inactive medicine) or a drug already being used for the condition. Importantly, both groups are matched so that 'confounding factors' are excluded. For instance, in a study looking at whether or not a medicine cut the risk of heart attack, it would be crucial for the two groups to have equal numbers of smokers or people suffering high blood pressure or raised cholesterol.
Earlier this year, a study looking comparing over 4,000 women - half with ovarian cancer, half without, was published (ref 1). In the study, women were asked if they applied talc to their genital/rectal area directly, on sanitary napkins, tampons, or onto underwear. They estimated how much talc they had applied over the years, and concluded that using talc was associated with a 33% higher risk of developing ovarian cancer, with a trend for increasing risk depending on how long, or how often, women used it for. They suggested the risk was amplified for non-smokers, pre-menopausal women, especially if they were heavier or didn't smoke, and for women who used HRT after the menopause. This was particularly true for certain types of ovarian cancer.
So far, so shocking - but there are lots of caveats in this study. Firstly, it was a 'retrospective' study - it asked women to think back and remember how much talc they had used. A well-recognised phenomenon called 'recall bias' may come into play here. Women in the USA would almost certainly have heard about the possible link between talcum powder use and ovarian cancer, because it has been in the news for some time. Women diagnosed with ovarian cancer might be more likely to remember using it, or to overestimate how much they had used. You can get round this potential skewing of the data by using 'cohort studies', which follow groups of women to see if they develop cancer. The only study of this sort which has looked at talcum powder use didn't find any link with cancer (ref 2)
Secondly, women who used talc were more likely to be heavier. In my clinical experience, this is hardly surprising - heavier women tend to sweat more, and use talc to stop chafing. Being heavier is recognised as a risk factor for ovarian cancer (ref 3) - so this may have affected the results
Finally, the numbers involved were very small - even among women at highest risk, there were just 41 cases over 24 years. Most doctors are dubious about the results of small studies, especially this sort of retrospective study, because there is a much great opportunity for the play of chance to alter conclusions.
The American Cancer Society does point out that in the past, some talc contained asbestos, which is conclusively proven to increase the risk of some cancers. However, they also make clear that 'All talcum products used in homes in the United States have been asbestos-free since the 1970s.' So what should we do about it? If you have used talcum powder in your nether regions in the past, you certainly shouldn't panic. But until we know more, I would suggest erring on the side of caution. Apart from feeling just a bit more sweaty, there are no known risks from avoiding talcum powder - and I'm a firm believer in better safe than sorry.
1) Cramer DW, Vitonis AF, KL Terry, et al. The association between talc use and ovarian cancer: a retrospective case-control study in two US states. Epidemiology 2016;27(3):334-46
2) Gertig D et al. Prospective Study of Talc Use and Ovarian Cancer. J Natl Cancer Inst (2000) 92 (3): 249-252.
3) Bandera E et al. Obesity, weight gain, and ovarian cancer risk in African American women. IJC 2016 DOI: 10.1002/ijc.30115