How worried should you be when
something gets slapped with the label “probably courses cancer”. It’s a
classification that makes for easy headlines, as chemicals that were
previously thought to be not so bad, are outed a seemingly potential killers. Yet as we’ll see, just because
something might cause cancer, doesn’t mean that it necessarily will.
One of the more prominent organizations that evaluate
carcinogens is the International Agency for Research
on Cancer, or IARC for short. IARC publishes doorstop
sized reports – they called the monograms – that evaluate the evidence for, or
against, something having the ability to cause cancer. These monographs are the culmination of
a long and arduous process. Leading experts huddle
together for days at a time, and carefully sifted through publicly
available data. They look at whether there’s evidence
for a specific agent causing cancer in people They look to see if there’s any evidence
for causing cancer in animals. They examine whether there are scientific
reasons to think it might cause cancer. And they weigh the evidence, which is
really the black and white, to determine whether, on balance, there’s
a chance that the agent could cause cancer, given the right circumstance. At the end
of this process, the substance or agent under examination
is given a number from 1 to 4. First,there are the group one substances. These are the bad actors
where the data are pretty clear that exposure to enough of them could lead to cancer. At the other end of
the spectrum, There’s group four. This is where they put the stuff where the balance of evidence suggest that they don’t cause cancer. Just above this is
group three. Here you’ll find substances where there just isn’t enough evidence to indicate that they are carcinogenic. and then there’s group two. Group two is
the tricky one. These are the substance where there are
hints that they might cause cancer, but the data aren’t conclusive. Group two is
divided into “probable carcinogens” and “possible
carcinogens”. If there’s evidence that a substance can
cause cancer in animals, but the jury’s out on humans, it’s likely to be labeled as a possible
carcinogen, and placed into group 2B. On the other hand, if the date on
cancer in humans is just a little stronger, but still not conclusive, the substance is likely to be put in
group 2A, and labeled a probable carcinogens. In
effect, ending up in group 2 is equivalent of
the IARC slapping a “take care” label on something. They’re letting you know
that, under some circumstances, if you’re exposed to enough of the stuff, you might get cancer. Plenty of common
substances end up with this “take care” label. Eat fried food for
instance, and you probably ingesting acrylamide; and IARC probable carcinogen. Spray weeds
with the herbicide Roundup, and you’re using the IARC labeled probable
carcinogen glyphosate. Interestingly, working as a hairdresser, and
working shifts that disrupt your body’s rhythms are also both listed as probable
carcinogens. Then there’s coffee, gasoline, and wait for
it, pickled vegetables. Each of these are listed by IARC as possible carcinogens. In effect an IARC label
indicating something is a potential or probable carcinogen, doesn’t mean that it will necessarily
cause cancer. And it certainly doesn’t mean stop
using it. The label is only half the story. It suggests what
*could* happen, but it doesn’t indicate how likely it is.
It’s the equivalent of saying a rock could kill you, but not pointing out
that it probably needs to be dropped on your head for a great height first! To make sense if these labels, additional
information is needed on what “probable” actually means, together with
how much stuff people are exposed to, and how much if it is needed to cause
cancer. In other words, the label alone shouldn’t
worry you. We’re exposed all the time to substances
that may cause cancer – that’s unavoidable. But neither should IARC labels be taken
lightly. They indicate what might be a problem.
The real challenge – and this is where risk assessment comes in – is working out how to prevent that “might
be” from turning into an “is”, either by keeping exposures to safe
levels; replacing the substance with something less harmful; or getting rid of it altogether. That,
though, is a decision that needs more information than just IARC assessment can provide.