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.