The International Agency for Research on Cancer (IARC), part of the World Health Organisation, has reclassified talc from “possibly” to “probably” carcinogenic, and reclassified acrylonitrile from “possibly carcinogenic” to “carcinogenic” to humans.
Acrylonitrile is used in the manufacture of acrylic and modacrylic fibres for use in clothing and textiles, carpets and upholstery, reports Medscape. It’s also used in many industries to make certain plastics, rubbers, and chemicals, and in the past, as a pesticide, and it’s present in cigarette smoke and air pollution.
At a meeting last month in France, 29 scientists from 13 countries that comprise the IARC working group upgraded talc to “probably carcinogenic to humans” (Group 2A) based on a combination of “limited” evidence that talc causes ovarian cancer in humans, “sufficient” evidence for cancer in experimental animals, and “strong” mechanistic evidence in human primary cells and experimental systems.
The upgrade supersedes the 2010 classification of talc not containing asbestos or asbestiform fibres and perineal use of talc-based body powder as “possibly” carcinogenic (Group 2B).
Talc containing asbestos category was not re-evaluated and retains its carcinogenic (Group 1) classification.
In a Lancet Oncology online report published earlier this month, the working group wrote that since 2010, “more consistent positive associations” for ever-use versus never-use of talc have been reported in pooled cohort studies and case-control studies, including evidence of an exposure-response relationship with frequency or duration of use.
However, they couldn’t rule out bias from differential exposure misclassification or confounding by asbestos contamination of talc.
Kevin McConway, PhD, with the Open University, United Kingdom, helped clarify what the IARC classifications mean.
“In the case of talc, there isn’t a smoking gun that its use causes any increased cancer risk,” he said in a statement from from the non-profit organisation Science Media Centre.
In other words, the experts “aren’t saying that talc cannot cause ovarian cancer in humans, but they can’t at all be sure that in fact it does cause an increase in risk, at the levels of exposure that might happen in normal use of talc or indeed in any other circumstances of use”.
Overall, there’s still a lot of uncertainty on this, he added. “So we're in the rather unsatisfactory position that IARC experts say that using talc can probably cause cancer in humans under certain circumstances that they don’t define.”
Paul Pharoah, PhD, DPH, professor of Cancer Epidemiology, Cedars-Sinai Medical Centre, London, found the evidence for the carcinogenicity of talc in humans “extremely weak”.
“Many observational studies have shown an association between talcum powder use in the genital area and ovarian cancer risk,” he said.
“However, such a correlation may easily be explained by other factors that are associated with both talc and with ovarian cancer (so-called confounders). Moreover, the reported associations with different types of ovarian cancer – which are known to be very different in their risk factors and underlying biology – are not consistent with the observed association being causal.
“Overall, my interpretation of all the evidence is that women who have used genital talc in the past should not worry about their future risk of ovarian or other cancers,” Pharoah said.
The working group’s upgrade of acrylonitrile to “carcinogenic” to humans (Group 1) was based on “sufficient” evidence that it can cause lung cancer, as well as “limited” evidence for bladder cancer.
The evidence stems mainly from studies in workers producing or using acrylonitrile. There was sufficient evidence for cancer in experimental animals and strong mechanistic evidence of key characteristics of carcinogens in experimental systems, the group said.
The Lancet Oncology article – Carcinogenicity of talc and acrylonitrile (Restricted access)
Medscape article – WHO Upgrades Carcinogenicity of Talc and Acrylonitrile (Open access)
See more from MedicalBrief archives:
Purity & Elizabeth Anne recall baby talcs after asbestos trace levels found
J&J confirms end to global talc sales amid contamination litigation
Largest J&J talc damages award over ovarian cancer claim
E-cigarettes less toxic and safer than conventional cigarettes