Part 2 of IARC’s Talc Journey

Part 1 of this exposé showed how IARC’s three talc monographs came to different conclusions even though the evidence and studies did not change. The main reason for the differences (and the motivation for a third talc monograph) was the 2019 update to IARC’s Preamble, the document which sets the guidelines for classifying substances as carcinogens. The international cancer agency essentially moved the goalposts to ensure that substances like talc could be confidently classified as Group 2A – probably carcinogenic. Part 2 will focus on how some IARC talc working group experts did not agree with the conclusions and how IARC managed this dissent.

The scientific method demands that any hypothesis or theory should be rigorously challenged. As Karl Popper argued, the more a scientific position can resist falsification attempts, the more robust it becomes. So it is quite normal to see scientists disagree, often quite heatedly. If you have five scientists in a room, it is not unusual to have six scientific hypotheses. While consensus is politics, challenging the consensus is science.

Sadly, part of the attack on scientific establishments has been the undermining of the scientific method, trying to force a consensus for political purposes rather than to advance discovery, dialogue and development. The climate debate was polluted with the isolation, exclusion and delegitimisation of sceptics by a pre-ordained, politicised consensus community that controlled funding mechanisms, academic positions, publishing institutions and the media. The term “sceptic” became an insult hurled on researchers when, in reality, it is what all scientists should be. Similar oppressive consensus coalitions are forming around food sciences, chemicals and plastics where challenging the orthodoxy of “the science” will threaten researchers’ careers.

The IARC Consensus Process

No organisation has brutalised the scientific method more than the International Agency for Research on Cancer (IARC). They have published 139 monographs, tens of thousands of pages, and there seems to have been no discussions of dissenting views. Imagine how dozens of scientists can stay in a room for a week in Lyon, France, and manage to consistently agree with each other. This is either a miracle of science, good wine or a contrived stitch-up orchestrated by a certain politically motivated class of activist scientists.

Some may argue that IARC merely produces hazard assessments so they are not at all scientific. All their monographs have to do is prove that it is not impossible for a substance like talc to be a carcinogen (without determining exposure levels or likelihood of a substance actually being a carcinogen). The reason IARC has never published dissenting views, they may claim, is because it is very difficult, with certainty (given the parameters the IARC monograph team have set for themselves), to argue that something could not be a carcinogen.

But IARC also has to determine if there is sufficient evidence for carcinogenicity (Group 1), probably carcinogenic (Group 2A) and possibly carcinogenic (Group 2B). It beggars belief that all of the scientists in the room can agree on all points. IARC does not report on dissenting views during the monograph panel discussions.

Producing an IARC monograph is a controlled process. Most of the document is written in-house before the panel of experts arrive in Lyon for the week-long meetings. As Kate Kelland revealed in a Reuters exposé, the monograph conclusions can be edited and changed after the working group members have gone home. Panel members have been instructed to not release any email correspondence or publicly share elements of the discussions that took place during the meetings. Often IARC chooses loyal scientists they like working with as the same names keep showing up on working group panels (too often, they are Collegium Ramazzini fellows who use the cancer agency to support lucrative side-jobs like litigation consultants). “Transparent” and “Open” are not words that would describe the IARC monograph process.

But a panel member on IARC Monograph 136 (the third monograph on talc) did speak out in disagreement with the cancer agency’s conclusions and it revealed just how managed and unscientific the IARC process is.

Abstaining or Dissenting?

Andrew J. Ghio, from the U.S. Environmental Protection Agency, was a member of the third IARC talc monograph panel that met in 2024. He wrote a letter to the editor to the American Journal of Respiratory and Critical Care Medicine in February, 2025. As a reminder from Part 1 of this exposé, the third talc monograph concluded that talc was probably carcinogenic (Group 2A) differing significantly from the 2010 IARC monograph classification of talc, not on the basis of any new research or evidence, but because IARC had updated their Preamble – the rules for determining the carcinogenicity of a substance. Ghio confirms that view:

As a member of this working group, I suggest that this conclusion conflicts, in part, with a previous IARC classification that provided that inhaled talc not containing asbestos or asbestiform fibers was a group 3 carcinogen (“not classifiable”), while perineal use of talc-based body powder was a group 2B carcinogen (“possibly carcinogenic”) (2). These evaluations were conducted by two working groups that included some of the same experts who reviewed much of the same data (1, 2). The dissimilar conclusions of the two groups may reflect the impact of an amended IARC monograph preamble, delivered between the two classifications, that was intended to provide a stronger and more transparent method for the identification of carcinogenic hazards (3).

Ghio even added that not only was the evidence the same, but the 2010 and the 2025 talc monographs had many of the same experts on the working groups.

Part 1 of this exposé noted that the 2019 update to the Preamble included redefining “sufficient evidence” to include evidence from single animal studies and the codification of the Ten Key Characteristics of Carcinogens (based on an article published a few years before by a collection of IARC insiders). The Preamble update allowed for a probably carcinogenic classification (Group 2A) if it included two of the following:

• sufficient evidence from at least one animal study;
• several Key Characteristics; and
• limited evidence of carcinogenicity in humans (what IARC normally would consider as possibly carcinogenic – Group 2B).

But were the elements in the IARC Preamble update credible enough to justify the new classification of talc without asbestiform fibres as probably carcinogenic? Ghio was not convinced.

“Several experts did not agree with the reclassification of talc on the basis of the single animal study and an inadequacy of meeting a majority of the key characteristics and, accordingly, abstained from voting on the carcinogenicity of talc.”

There are so many questions here. Who else abstained from voting and why did IARC not consider this? IARC did not report this. If a panel member abstains from voting, is that the same as dissenting? It seems that IARC does not have a policy on publishing dissenting views like other scientific agencies? How many abstentions would require a change in the monograph text or carcinogen classification?

Why did Ghio (and others) disagree with the Preamble update’s sophistry?

The preamble stipulated that “Exceptionally, a single study in one species and sex may be considered to provide sufficient evidence of carcinogenicity,” and the working group subsequently accepted a single (positive) animal study to provide sufficient evidence of carcinogenesis (4). Previously, IARC and others had considered this same study to possibly lack relevance in the issue.

Part 1 showed how the second IARC talc monograph working group considered the 1993 National Toxicology Program talc animal study as inadequate and irrelevant in 2010 and then, mysteriously, it was the only animal study used to justify sufficient evidence for carcinogenicity in the third talc monograph in 2025. Like any credible scientist, Ghio rightly could not accept this flipflop.

Ghio and other working group members were also not convinced that two Key Characteristics (“inducing chronic inflammation” and “altering cell proliferation”) were sufficient for the Group 2A classification. Ghio argued that “altering cell proliferation” comes from chronic inflammation. He criticised IARC for misinterpreting the Preamble update to argue that two out of the ten Key Characteristics was sufficient for the cancer agency to force their conclusion.

IARC Failed to Report the Dissent

There was no mention at all in the final IARC monograph of the scientists who disagreed with IARC’s attempts to classify talc as probably carcinogenic. IARC would want the world (or at least the juries in US talc lawsuits) to think that their third talc monograph classification represented a clear “scientific” consensus. From Ghio’s letter and his cogent arguments, it is evident there was no consensus. The main reason for Ghio’s letter to the journal was to advise the medical community to ignore the IARC talc monograph conclusion when deciding on using talc in pleurodesis procedures as it is safer and more effective than alternatives.

Reading through IARC’s third talc monograph publication, it was sad to see how the cancer agency was trying to paper over the dissent to their conclusions and their woeful update to the IARC methodology. For example, on page 434 of Monograph 136, IARC confidently claims:

There is strong evidence that talc exhibits key characteristics of carcinogens. The evidence is based on consistent and coherent evidence that talc induces chronic inflammation in experimental systems, and alters cell proliferation, cell death, or nutrient supply in human primary cells and experimental systems.

It did not seem to matter to the publisher of this monograph that a number of scientists participating in the working groups did not share IARC’s level of confidence. This is not science. But it raises some important questions:

• Does every IARC monograph try to cover up dissent to pretend they are representing a scientific consensus?
• Why has this issue of widespread IARC panel dissent not drawn attention before?
• Is there any credibility or value to such political consensus fabrications?
• Is the week-long monograph meeting process just an expensive circus pretending to project scientific authority?
• Wouldn’t it help IARC’s dismal reputation if they admitted there was disagreement among the world’s cancer experts and present where there is a need for further studies?
• Who benefits from such a cynical, pre-ordained consensus process?

Part 3 will look at the special interests behind the IARC monograph process, made all too evident with the third talc monograph, that seemed hell-bent to deliver a “probably carcinogenic” classification.

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