During the extensive media coverage of the sad and untimely death of Dana Reeve from lung cancer, I was intrigued by the many experts who were interviewed on national news shows or in the newspapers and magazines proclaiming there was an epidemic of lung cancer in non-smokers.
Invariably, the comment was made that lung cancer was becoming a particular problem for non-smoking women compared to men who were non-smokers. This comment would then be followed with a series of theoretical discussions as to why this was the case, including genetic differences, hormonal susceptibility, and so on.
When reporters would speak to me, I told them I couldn’t substantiate these differences, and I wasn’t going to guess as to why non-smoking women were more susceptible to lung cancer than non-smoking men.
I can tell you I wasn’t comfortable with my apparent ignorance. As it turns out, I may not have been so ignorant after all.
This week, colleagues of mine from our epidemiology department at the American Cancer Society and the University of California San Diego published an article in the Journal of the National Cancer Institute which is the most definitive analysis of lung cancer incidence in non-smokers.
Their conclusions? Non-smoking men are at greater risk of getting lung cancer than non-smoking women, and non-smoking African American women have a greater chance of dying from lung cancer than non-smoking white women.
This discussion is important because lung cancer is the leading cause of cancer death in this country. Of the people who die from lung cancer, somewhere around 85-90% of them are either smokers or former smokers (in fact, in the United States today there are now more former smokers than current smokers).
That means there are still many thousands of people in this country every year who die from lung cancer even though they never regularly smoked cigarettes. My colleagues estimate this number is between 17,000 and 26,000 deaths a year from lung cancer in non-smokers.
The cause of these deaths, for the most part, has been attributed to a number of factors including second-hand smoke, smoking other forms of tobacco products, exposure to other carcinogens, and occupational, environmental and even medical exposures.
At various times over the past 45 years, the American Cancer Society has studied about 2.2 million people who have participated in two long term programs called CPS (for Cancer Prevention Study) I and CPS II. These folks have been followed for many years, and their various habits, medications, and disease status have been reported and analyzed. Their causes of death have been recorded and verified for accuracy.
What makes studies of this type so important is that the participants provide information prospectively. That means we look at the people going forward, not retrospectively where we take a look backwards to figure out what the facts may be.
There is a lot less bias and much better recall of information in prospective data gathering, and the results have enabled my colleagues to report many breakthrough studies on various cancer causes and relationships which have been considered critically important in our understanding about the causes of cancer.
For example, a study they reported a couple of years ago established the link between the role of being overweight and obese with the significantly increased risk of developing a number of cancers in both men and women. This breakthrough study allowed us to understand that obesity affects cancer risk just as it increases the risk of diabetes and heart disease, among other illnesses.
In the current lung cancer study, they examined the records from CPS I and II to find out how often lung cancer affects non-smoking men and women of both races.
Of the 2.2 million people who participated in the two prevention studies, 940,000 were non-smokers. The overwhelming majority of the participants were white.
The researchers found that in both studies the risk of dying from lung cancer was greater for non-smoking men than non-smoking women, although the differences were less more recently.
Although death rates from lung cancer for both sexes were higher in African Americans than whites, the only difference that appeared significant after making statistical adjustments was for increased rates of death in non-smoking African American women compared to white women.
Finally, there was no evidence that the rate of death from lung cancer in non-smokers has increased over time.
What does all of this mean?
Contrary to public perception and expert misinformation, there has been no increase in deaths from lung cancer in people who are non-smokers, and male non-smokers die more often from lung cancer than women.
This does not diminish the importance or the impact of lung cancers in non-smokers. Lung cancer is a serious disease, and if lung cancer in non-smokers was ranked as a cause of cancer deaths, my colleagues say that it would be the sixth to eighth most common cause of deaths from cancer.
Why would people, including the experts, think that lung cancer was a more important issue for non-smoking women than men?
There may be many reasons, but the reality is that there simply were not studies available that had the strength of numbers and duration of follow-up that the CPS studies provided. The researchers indicate in the article that it is difficult to obtain this information on as broad a basis as needed to ensure accuracy.
But there is another, perhaps more complicated reason why people have the perception that lung cancer is a more serious problem for women than men.
Historically, more men smoked than women. That in turn means there are fewer non-smoking men than non-smoking women. That means, numerically, there is a larger population of non-smoking women than men who would be susceptible to getting lung cancer. The net result is more women do die from lung cancer if they are non-smokers.
But that is not the way we measure risk. We measure risk by the number of people who die of a condition per 100,000 people (or men and women). And when we measure the risk of dying from lung cancers for non-smokers, it is the risk per 100,000 that is important. In this circumstance, the risk is higher for men than women.
As to why the situation is worse for African-American women than white women, we do not have an answer.
Unequal access to treatment, differences in diet and/or exposure to environmental carcinogens, differences in rates of tuberculosis (a disease whose scars can result in an increased risk of lung cancer) or possibly underlying genetic differences are all reasons the researchers offer to explain their findings.
As time goes on, and more men become lifelong non-smokers, eventually there will be a larger number of non-smoking men dying from this disease.
As I have mentioned previously in these blogs, we need to do a better job of understanding lung cancer, and how to treat it.
We need to acknowledge that for many the diagnosis of lung cancer is the result of an overpowering addiction that some have been able to overcome and others have not.
We need to acknowledge that we must do a better job of reducing the risk of lung cancer for both smokers and former smokers alike, and we need to do a better job of understanding the causes of lung cancer in non-smokers.
But in all of this understanding, we need to do a better job of getting our facts right. We need to be able to say, “I don’t know” when we really don’t know.
And, we should pay special attention to not letting our opinions get in the way of the facts, no matter how heart-rending the circumstance may be.
The American Cancer Society's Cancer Prevention Studies described in today's blog have been of incredible value in our understanding of cancer and its risk factors.
We are presently in the process of recruiting volunteers who are willing to participate in our new CPS-III study which is just getting underway.
Recruiting is ongoing at our Relay for Life events in communities nationwide.
If you are interested in learning more about CPS-III, and especially if you are thinking about volunteering for this study, please go to our website, email us at email@example.com, or call us at 1-888-604-5888.
If you want to help and if you qualify, you will be part of something very special.