November 18, 2022
“I’m in great physical shape. I’ve never touched a cigarette! How could I have lung cancer??” You hear this in online cancer discussion groups, Facebook groups, face-to-face support group meetings. It seems that, more and more, you hear this from women who also happen to have EGFR mutations. You’ve even heard it from me. What’s going on here?
We’ve talked about radon already– have you checked your house yet?? — and now we’re going to have a very sobering chat about air pollution.
Check any of the lung cancer websites for civilians, i.e., non-scientists, and you’ll see they all agree: air pollution is associated with lung diseases like lung cancer. Look even more closely and you’ll notice all of them step delicately around the fact that they don’t know why.
Until now.
In September 2022, at the conference of ESMO, the European Society for Medical Oncology, Charles Swanton MD PhD presented a new study out of Francis Crick Institute and University College London. In a video of a post-presentation discussion video, he couldn’t have been more clear:
…what this work shows is that air pollution is directly causing lung cancer, but through a slightly unexpected pathway.
He went on to describe that pathway.
A Path to Lung Cancer
Scientists have always figured that pollution causes cancer in the “classic” way: junk gets into the lungs, causes mutations in the cells, and thus, cancer. But as far back as 1947, Israeli biochemist Isaac Berenblum proposed that cancers needed not just a DNA mutation to form, but also an activator to trigger the process. Somehow, that work got lost in the scientific shuffle. But Swanton and his research team showed that Berenblum had been on to something big.
One of the things Swanton et al. knew they had to do was explain how cancer can be initiated without causing mutations.
Mutations in normal lung cells, specifically, exons 19 and 21, happen naturally with age. Remember, these mutations are not enough to cause cancer on their own. But say the person with these existing mutations breathes polluted air, specifically, air that’s laden with microscopic PM2.5 particles.
PM2.5 refers to atmospheric particulate matter (PM) that have a diameter of less than 2.5 micrometers, which is about 3% the diameter of a human hair. Diesel exhaust and the burning of fossil fuels and other agents– forest fires anyone? smoke from wood-burning stoves?– are among the things that produce PM2.5 particles.
So, you’re walking around with some normal mutations in your lungs. Maybe you’re going to the grocery store, or riding your bike somewhere. It’s a beautiful day; you take a couple of deep breaths in appreciation of fresh air. You don’t notice that in the air carries a gazillion invisible particles.
These microscopic particles get into the lungs, which release interleukin 1B. Interleukin 1B causes mutant EGFR cells to change to a stem cell cancer state. Stem cells can reproduce indefinitely. And so, the seeds of a cancerous tumor are sown. Swanton and his team showed that inhaling PM2.5 particles increases not only the number of tumors in mice, but the grade of the tumors as well.
How’s the Air Quality In Your Neck of the Woods?
I off-handedly started paying attention to the PM2.5 measurements in local air quality reports in 2020, when raging forest fires earned the Pacific Northwest the dubious honor of having the worst air quality in the world.
What I’ve noticed is that the overall AQI (Air Quality Index) can be in the green, yet, within that, PM2.5 measurements can be above what is considered safe in the World Health Organization Global Air Quality Guidelines. The graphic below shows you what I mean.
Overall, the 2021 air quality average in the U.S. was Good. Yay! But below the green “Good” rectangle, there’s a yellow rectangle. Half of the rectangle is goldenrod in color, with a large exclamation point alerting the astute reader that there’s something to be noticed here. Next to the goldenrod box, in a lighter shade of gold, we notice small letters and numbers reading PM2.5 and then, below that, in bigger, much darker typeface: x2.1. In case we miss the point, it gets spelled out for us. In 2021, the average PM2.5 concentration in the USA was 2.1 times the WHO annual guideline value.
So much for the Yale Medical Information sheet about lung cancer in nonsmokers. One of the questions in their handy FAQ format wonders What causes lung cancer in nonsmokers? They list four: radon gas (we’ve discussed that), secondhand smoke, cancer-causing agents at work, and finally, air pollution. Here’s what they say:
Air pollution: While scientists link indoor and outdoor air pollution to lung cancer, the risk of lung cancer from air pollution is believed to be low in the United States, where air quality is regulated, compared to many other countries in which it is not.
Swanton and his team would disagree.
Spend a little time exploring data under the tab World Air Quality on IQAir. Look at some of the live information about air quality in cities around the world. (Yes, IQAir is trying to sell you stuff, but I don’t get a cut. I just think the way they represent their information is cool.) If you go to their World’s Most Polluted Cities (historical data) menu item, you can filter the information to get a view of your state, etc.
Now What?
It would be easy to say, well, just don’t drive, ride your bike. Except, it’s hard to ride a bike without inhaling.
While we’ve heard about climate change since forever, this PM2.5 stuff has been in the periphery. Sure, it’s been a part of air quality reports– but as long al the AQI forecast was green, who cared? It turns out we need to care. A lot.
Meanwhile, we’ve already made decisions on a family and person level. We drive a hybrid car. We’ve always shut the windows when the AQI is bad; now it will be when PM2.5 numbers are bad, no matter what the reports are of overall air quality. Our furnace filters and forced air vents are at least MERV 13, and they should probably be higher.
Ever since the fires, we’ve run high-quality HEPA air filters in the house, one big one for the whole downstairs, one small one in our bedroom. It’s amazing how gunked up these are when we go to change the filters.
I have several air monitoring apps on my phone. My current favorite is IQAir, which sends me a notification about air quality at 8 a.m. every day. I use these reports to help me decide how active I’ll be outside. Mostly I opt for caution, but sometimes a girl’s just gotta ride her bike. (Besides, does it matter if I already have lung cancer?)
But there’s got to be action that can be taken on city, state, national levels. I don’t know yet what that will be. If you do, drop a note in the comments.
Meanwhile, thanks for reading. I hope you breathe some sweet air today.
P.S. FWIW, It’s a glorious clear day today. The sun is shining and there’s a brisk breeze, but it’s the kind of day you want to be outside. Portland’s air quality today is moderate (yellow) but its current PM2.5 level is 3.8 times (orange) the WHO air quality guideline value. How are things in your hometown?
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What’s New: May 2023
On May 9 2023, the International Association for the Study of Lung Cancer posted Air Pollution and Lung Cancer: A Q&A with Professor Charles Swanton on their website. Their summary:
During a recent interview with ILCN, Professor Swanton reviewed the possible mechanisms at play when particulate matter triggers cancer growth and discussed new data that sheds additional light on the process.
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