Why Lung Cancer is So Common and Who's at Risk

Lung cancer risks and causes and screenings

/ Author:  / Reviewed by: Joseph V. Madia, MD

Lung cancer is the second most prevalent serious cancer in the United States, after breast cancer in women and prostate cancer in men. However, it kills more women and men than breast, prostate, colorectal and pancreatic cancer combined.

According to the American Cancer Society, just over 225,000 Americans will be diagnosed with lung cancer this year, and 160,000 people will die from it. And about 27,000 of the people diagnosed with any type of lung cancer will never have smoked any form of tobacco.

To learn more about this disease, we conducted a telephone interview with one of the nation’s leading experts in the field – D. Ross Camidge, MD, PhD, the Director of the Thoracic Oncology Clinical Program at the University of Colorado.

We discussed a wide range of topics with Dr. Camidge, who offered interesting insights into the disease and the people who live with and die from it.

This conversation will be covered in a series of articles. In this first one, we look at risk factors, causes and screening for lung cancer.

Who is considered to be a smoker?

For the purposes of most studies, a never-smoker is defined as someone who has either never smoked, or smoked 100 or fewer cigarettes in their lifetime.

Smokers, therefore, are defined as people who have ever smoked more than a 100 cigarettes in their lifetime. However, the ‘smoking’ category is clearly diverse and is not just the difference between an ex-smoker (someone who quit more than a year previously) and a current smoker.

‘Light’ smokers are usually considered people who have smoked a pack or less a day for 10 years or less. In contrast, ‘heavy’ smokers are usually defined as having smoked at least a pack a day for more than 30 years, or the equivalent.

Often, smoking exposure is defined in ‘pack-years’ – a composite of years and number of cigarettes a day. For example, 30 pack years could be a pack a day for 30 years or 2 packs a day for 15 years, for example.

Obviously, there's a huge difference between someone who has smoked two packs a day for 40 years and someone who smoked five years in college and quit 30 years ago. But in some studies, they're all categorized together as simply ‘smokers’.

So any level of smoking is dangerous for you?

Yes, in terms of lung cancer risk, but there's clearly a continuum. About 50 percent of the people who are diagnosed with lung cancer were smokers and quit - often many years beforehand. For some people it could be 20 or 30 years previously.

So smoking is seen as the cause of lung cancer in someone who quit 30 years ago?

Yes. Because while it takes 10-12 years for the risk to approximate that of someone who has never smoked, the risks are never equal. The person who has ever smoked always has slightly higher risks.

And just to be clear, when quantifying risk by smoking exposure, I think it is appropriate to use this information to determine how to use our resources, for example, in determining who is at greatest risk and therefore in greatest need of lung cancer screening, but we should never use this information to play the blame game.

Everyone is deserving of consideration and care.

Are people who smoke pipe or cigars at risk? What about marijuana?

Yes, but the data is a little more scant. Essentially any tobacco exposure affects your risk of lung cancer. For some tobacco sources such as chewing tobacco, which produce different patterns of where the carcinogens linger, the exposure can also affect your risk of other cancers, such as cancers of the head, mouth and neck.

So who should be screened for lung cancer?

The only technology that's been proven to be effective in screening for lung cancer in people with no symptoms is called low-dose spiral CT (computed tomography) scanning. In the definitive study that looked at this technology, annual CT scans were compared to an annual chest x-ray in individuals who had smoked 30-pack years and were aged 55-74 years.

This study (the National Lung Screening Trial or NLST) involved 53,054 people and found that the low-dose spiral CT scan diagnosed more people with lung cancer than the chest x-rays did. Importantly, these cancers were early stage cancers and therefore were potentially curable.

In fact, in the NLST, there were 309 deaths from lung cancer among the people screened by chest x-rays, and 247 people who died from lung cancer among the people who were screened using annual low-dose spiral CT scans. So, according to this study, the CT scanning saved an extra 62 lives because it detected these cancers at a stage when they were still curable.

What this tells you is that conducting CT scans every year for people who are 55 to 74 with high smoking histories saves extra lives.

What it doesn't tell you is a) whether it is economically viable to do this (scans are expensive and the absolute number of lives gained is small – these are tough calculations to look at in black and white terms – but that’s what insurance companies and governments do all the time). And b) whether it would save any lives at all if you were looking in lower risk individuals such as younger people or those with lower or no smoking history.

Overall, the NLST probably isn’t giving us data on a definitive lung cancer screening tool. Instead it's just proof of principle that if you find cancer early enough you can actually impact survival, and therefore screening, in theory, really could save lives in lung cancer – if we can only get it to work better (i.e., make it both cheaper and more broadly applicable).

You're saying we really don't have any good lung cancer screening tests yet?

That's right - we're still a long way from having a really good screening test. And we clearly don't have any screening for people who aren't high risk in that they have no smoking history. If you're a never smoker, you've got nothing.

What about new technologies being used for screenings?

Other technologies are being developed to diagnose cancer in different ways.

Exhaled breath. These include the so-called "nano-noses" which look at the exhaled breath. The argument is that cancer cells metabolize nutrients in a slightly different way from normal cells. And if you have a sensitive enough test, you could detect those broken down products and could find them maybe in exhaled breath.

There's some provocative early data. Obviously it would be very attractive if you could blow into a bag and have it analyzed. But we have to see the definitive data.

Again, it will be interesting to see if it works and whether it will be a useful test just for those at very high risk based on smoking history, or if the breathalyzer approach is something that will be able to detect any lung cancer, located anywhere in the lungs, or maybe even any cancer anywhere in the body.

If we could make it so simple, such non-invasive technology could rapidly become part of a person's routine medical care.

Of course, that's what we all hope. But unfortunately, we need data to support the hope.

Blood tests. Other people are looking at blood tests. They want to know if there are particular signatures in the blood or the presence of specific abnormal cells in the blood that could detect cancer.

As we're recognizing in the therapy arena, lung cancer isn't one disease, it's multiple different diseases. Will we be able to detect all types of lung cancer or all types of any cancer with a single test? I doubt it.

Or will we have to multiplex the diagnosis to detect all the different cancers? This is what I think, but only time will tell.

If smoking rates are going down in this country, why is lung cancer still far and away the most common cause of cancer death in the United States today?

Firstly, not all lung cancers are related to smoking. What’s driving cancers in non-smokers is still largely a mystery.

And secondly, there's an incubation period for smoking-related cancers of at least 10 years. So if you stopped smoking today, it would take about 10 years before your risk drops down to approximate that of someone who has never smoked.

Those aren't exact numbers. The implication is that if you set the cancer in motion today, it may take 10 years to manifest. And that's not a steady rate of cancer development—it can accelerate at times.

This is why even though the smoking rates have changed, we haven't yet seen a real difference in lung cancer rates.

Of all the different types of lung cancer, how many do you think are being caused by something other than smoking? What causes these cancers?

Depends on what country you're in, but in general we think between 10 and 15 percent of lung cancers are reported in people who have never smoked. We don’t really know why these people are getting lung cancer.

There are theories about radon gas, cooking oils and other fuels. We do know that diesel exhaust exposure can contribute to the development of cancer.

However, we do not know exactly what causes lung cancer in people who have never smoked.

Next up – how to get the best care

In future conversations, we’ll discuss how people with lung cancer can get the best care and the most recent breakthroughs in cancer research.

Review Date: 
July 25, 2012