A vast body of information and research has grown regarding cancer. But for several decades, the illness was at best a mystery. This gave rise to knowledge-seeking organizations such as the International Agency for Research on Cancer (IARC).
In the mid-1960s, a group of French public figures convinced their president to form an organization with the purpose of exploring cancer. IARC eventually formed as a branch underneath the World Health Organization. Since then, the group has made bold claims such as processed meats being probably carcinogenic to humans. It might be worthwhile to explore how these classifications are made and the weight they carry.
The first part of the process is deciding what to evaluate. The group investigates a broad range of possible cancer-causers (commonly called agents). These range from personal habits to chemicals, primarily from occupational and environmental exposures. IARC has a community of experts that prioritizes what to evaluate.
After an agent is settled upon, an evaluation is carried out by a Working Group formed of experts on the topic. In a similar fashion to deciding the next pope, they have their own conclave and gather for eight days in Lyon, France. They first break out into four groups and independently evaluate the following components: (1) situations of exposure; (2) epidemiological evidence (looking for relationships between exposure and cancer in broader populations); (3) experimental studies on animals (directly exposing an animal to the agent and measuring the outcome); and, (4) a mechanistic investigation (how does the agent lead to the development of cancer). It could almost be reduced down to the where, when and how between cancer and the agent.
The groups then reconvene at the latter part of the meeting and form a consensus on how the agent should be classified. The results and reasoning are then published in what is called a monograph. Within hours of the release, a wave of far-reaching media stories follow it.
IARC is considered by some to be a credible and influential voice for cancer. But the outcome of classifications often morph into crazy claims, such as, “Processed meats rank alongside smoking as cancer causes.” This is because when IARC classifies an agent, they do not evaluate risk. They make a ruling based on hazard.
Risk would be the probability of causing cancer. Hazard is if it has the potential to cause cancer. This is an imperative difference that rarely ever makes it into those far-fetched articles. IARC is transparent about its classification process and this distinction. But in the age of 140 characters or less, this detail is omitted in the echo chambers of the internet. For this reason, you will find the likes of sunlight exposure in the same category as smoking, despite the extreme difference in associated risks.
With the review of more than 900 agents in the past 50 years, only a single one of them was classified as probably not carcinogenic to humans. If IARC decides to evaluate something, you’re likely to hear stories about that item causing cancer. IARC plays a role in being a knowledgeable and scientific-oriented group when it comes to cancer-related hazards. But we should take the outcomes with a grain of salt—which, incidentally, also happens to be slated for review by IARC.