Lung cancer is America’s deadliest cancer, claiming about 125,000 lives each year.
It also remains exceptionally hard to treat. Despite significant progress in developing new medicines, fewer than three in 10 patients are alive five years after receiving a diagnosis.
For generations, the disease has been viewed as almost inseparable from cigarette smoking.
Yet as tobacco use has declined sharply, physicians are increasingly diagnosing lung cancer in people who have never smoked. The trend has prompted fresh questions about less visible threats that may be raising the risk for Americans.
A Daily Mail review of federal data has now highlighted one compelling factor: a person’s location may play a major role.
The county-by-county map above reveals an expansive cluster of lung cancer hotspots across much of the South and Midwest, in contrast with far lower rates across broad areas of the West.
Scientists are working to explain the disparity, examining potential contributors ranging from naturally occurring radioactive gas inside homes to pollution, genetic factors and exposure to second-hand smoke.
What is driving this stark national divide in lung cancer, and could overlooked hazards in your home or community be increasing your risk?
Smoking remains one of the most straightforward explanations.
Cigarette smoking has plunged nationwide over recent decades. In the 1960s, 42 percent of US adults smoked; by 2022, the share had fallen to only 11.6 percent.
Lung cancer rates have followed, falling by around 30 percent since 1992. But the relationship between the two is not immediate.
Cigarette smoke contains thousands of chemicals, dozens of which are known to cause cancer.
Repeated exposure damages the DNA inside lung cells, allowing mutations to accumulate over many years until cells can begin multiplying uncontrollably and form a tumor.
Smoking remains linked to around 80 percent of lung cancer deaths in the US.
Crucially, quitting does not wipe out that risk overnight. It takes around 10 to 15 years for a former smoker’s additional risk of lung cancer to fall by half compared with someone who continues smoking.
That means America is still living with the legacy of generations who smoked when the habit was far more common. And that legacy is clearly visible on the map.
The states where smoking remains most common are also among those suffering the highest rates of lung cancer.
West Virginia and Arkansas, for example, are among the states with the highest smoking rates in America – and also among those with the highest rates of lung cancer.
By contrast, Utah and California have some of the country’s lowest smoking rates and some of its lowest lung cancer rates.
But there are intriguing exceptions to the pattern – suggesting smoking may not be the whole story.
One potential explanation lies beneath the ground.
Radon is a colorless, odorless radioactive gas produced naturally as uranium in rocks and soil breaks down. It can seep through cracks and gaps in buildings and, in poorly ventilated homes, accumulate to dangerous levels.
Despite being young, healthy and a former Olympic ice hockey player, Rachael Malmberg was diagnosed with stage four lung cancer. The Minnesota native – had never smoked – believes exposure to radon gas, the second-biggest cause of lung cancer nationally, led to her disease
Malmberg is shown above with her daughter and partner. She said her discovery of high radon levels at home led neighbors to test their houses, which also revealed they had high radon levels
When inhaled over many years, radioactive particles from the gas can damage cells lining the lungs, potentially triggering cancer.
It is already considered the second-leading cause of lung cancer in America after smoking, responsible for an estimated 21,000 deaths from the disease each year.
And, crucially, exposure also varies dramatically depending on where you live.
Federal data shows the highest-risk radon zones are concentrated across large parts of the Midwest, Northeast and Northwest – including some areas with high lung cancer rates.
Of the ten states with the highest proportion of counties in the most dangerous radon category, Maine and Indiana are also among the ten states with the highest lung cancer rates.
And of the 24 US counties where lung cancer rates are still rising, 11 – almost half – are in the highest-risk radon zone.
But the relationship is far from straightforward.
Dr Amit Mahajan, a pulmonologist and spokesman for the American Lung Association, said: ‘If you look at areas in the Midwest and the upper Northwest, you see higher exposure to radon.
‘That doesn’t necessarily equate to the development of lung cancer, but it is a driver of lung cancer in nonsmokers. It happens via exposure that takes place over decades.’
Perhaps most intriguingly, some parts of the West have high radon levels but remarkably low rates of lung cancer.
Mahajan believes one explanation could be how Americans live in different parts of the country.
‘In colder areas, such as Maine and Indiana, which have both high radon exposure and high lung cancer rates, people will close up their houses for the winter months, which can lead to radon levels rising in the home, posing a greater risk,’ he said.
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‘But in warmer areas, such as California, where radon exposure is also high but lung cancer rates are among the lowest in the country, people may keep their homes open year-round, reducing the build-up of the gas.’
The worrying part is that it isn’t easy to tell if you are being exposed.
Radon cannot be seen, smelt or tasted, meaning dangerous levels can accumulate inside a home without its occupants realizing.
The only way to know is to test. Home radon testing kits are widely available and can cost as little as $20.
For Rachael Malmberg, the danger lurking inside her home only became apparent after she was diagnosed with stage four lung cancer at just 31.
The former Olympic ice hockey player from Minnesota had never smoked and was young, fit and healthy when she developed the disease.
Searching for an explanation for her diagnosis led her to radon. She tested her home and discovered levels of the radioactive gas were dangerously high.
Malmberg is pictured online during her treatment in 2017. She was eventually declared cancer-free
Malmberg had a radon mitigation system installed to remove the gas – and urged her neighbors to test their homes, too.
Three did. All three also discovered high radon levels.
Experts say stories like hers underline why testing is so important. Because radon has no color or smell, there is no way to know whether it has accumulated inside a home without measuring it.
Radon, however, is not the only environmental threat researchers are investigating.
Another is the air Americans breathe.
Tiny particles produced by cars, factories and other sources of pollution can be inhaled deep into the lungs, where they can damage cells and trigger inflammation.
Of particular concern is PM2.5 – particles so small they can penetrate deep into lung tissue and have been linked to lung cancer.
But here, too, the geographic picture is complicated.
Air pollution has fallen dramatically across the US in recent decades, dropping 78 percent since the 1970s. And today, some of the highest levels of PM2.5 are found in the West – the very region where lung cancer rates are lowest.
Of the 17 states with the highest PM2.5 levels, just two – Indiana and Ohio – are also among the ten states with the highest lung cancer rates.
Mahajan said this suggests pollution is unlikely to explain the stark divide on its own.
‘With air pollution, it is more likely that it will exacerbate or cause people to develop other conditions such as emphysema or asthma,’ he said.
‘But being exposed to air pollution doesn’t mean you have a higher risk of lung cancer per se. It’s more the cumulative effect of that plus other risk factors, such as smoking.’
And some people may be more vulnerable to lung cancer because of factors they are born with.
Scientists have identified a number of genetic mutations linked to the disease, including changes to a gene known as EGFR, which normally helps control how cells grow and divide.
When EGFR becomes mutated, it can cause cells to multiply uncontrollably, potentially leading to cancer.
These mutations are particularly important because they are disproportionately found in lung cancer patients who have never smoked.
There is also a striking ethnic divide.
Studies suggest EGFR mutations are found in around 39 to 51 percent of Asian lung cancer patients, compared with roughly ten percent of those of European ancestry.
Scientists do not yet fully understand why – or whether there is any way to identify healthy people at particular risk before cancer develops.
Other threats are better established.
Regular exposure to second-hand cigarette smoke has long been known to increase lung cancer risk, even among people who have never smoked themselves.
What remains much less certain is the long-term impact of vaping.
E-cigarettes have not existed for long enough for scientists to establish whether they cause lung cancer, a disease that can take decades to develop. But the American Lung Association says it is ‘very troubled’ by emerging evidence about their effects on the lungs, noting that e-cigarette vapor can contain potentially toxic substances.
For Mahajan, the emerging evidence points to a much more complicated picture of America’s deadliest cancer than was once believed.
‘We are seeing more lung cancer cases in patients who have never smoked, but it is hard to tell whether this is an increase or just because we are getting better at identifying the disease,’ he said.
‘In the past, we’ve been much more focused on just smokers. But it is clear that that picture is changing.’