When I joined GRACE earlier this month, a question was posed by a reader regarding whether there is an increasing frequency of the diagnosis of lung cancer in women who have never smoked. This is a very interesting question that those of us who specialize in lung cancer frequently wonder about.
We know that the vast majority of lung cancers in both men and women are caused by tobacco. Overall however, approximately 10% of lung cancers occur in never-smokers of both genders. In women more like 20% of lung cancers occur without a history of tobacco use. Other known risk factors for developing lung cancer, particularly in lifetime nonsmokers, include exposure to secondhand tobacco smoke (the most common reason, either through exposures in the home through a spouse or from parents when a child is growing up) or radon exposure. Asbestos is an agent that more frequently causes mesothelioma, but also increases lung cancer risk. In Asian countries, links have been drawn between certain cooking oils in poorly-ventilated homes and lung cancers. Heavy metal exposures such as nickel and cadmium have been tied to lung cancers, generally for people involved in the mining and heavy metal industries. Associations with diesel exhaust and other environmental air pollutants have been posed, as well.
The trouble with most studies looking at the “other” causes of lung cancer is that in most cases the results of the epidemiologic studies are clouded by the fact that many people evaluated have also had a smoking history. This makes the act of piecing together which compounds cause lung cancer on their own versus which are made worse by tobacco, or are completely unrelated, very difficult.
Statistics regarding cancer incidence and cancer deaths in the United States are published every year. We have finally seen a decrease in the incidence and death rates in men with lung cancer over the last several years. This has reflected the overall decrease in tobacco use. Women as we know have been slower to give up tobacco, but usage rates are also declining. Thus over the last several years, although we have not yet seen a decline in the incidence or death rates in lung cancer among women, we are at least seeing a plateau, or leveling of the curves.
Unfortunately what we do not have is comparable statistical information regarding how many of these patients, and what proportions, are never smokers. We know that the majority of lung cancers are now diagnosed in former tobacco users (thanks to the increasing quit rate), but we do not have a measure from year to year of the never smokers.
It is postulated that women are more susceptible to developing lung cancer than men are, and that relatively lower amounts of tobacco or other carcinogen exposure cause lung cancer in women compared to men. This may be related to hormonal differences between men and women, and is supported by evidence that women taking hormonal replacement therapy have worse outcomes with lung cancer compared to women who are not taking hormone replacement.
In my practice, it seems that more than 10% of patients are never-smokers, although this incorporates both men and women. However, as a subspecialist practice focusing on lung cancer, this may not be representative of what is occurring across the country. People who are never-smokers tend to have fewer health problems overall and are more able to seek out subspecialist care.
It may be that we are seeing more lung cancers in never smokers as the smoking-related lung cancer rates start to decline. It may also be that, finally, lung cancer is gaining greater awareness and advocacy, and that people who have lung cancer are now speaking out and telling their stories in a more visible way. More people than ever are living longer with lung cancer, and more people who have never smoked are fighting against the social stigmas wrongly assigned to lung cancer and are helping to raise awareness.
Currently we don’t have the dedicated statistical trials in US-based populations to know for certain. Hopefully as awareness increases, we will start to have this information reliably tracked in order to monitor the occurrence over time.
Given that in many never smokers currently we are unable to identify a specific exposure that caused the lung cancer, having more reliable epidemiologic data in the future may help us more successfully track down, and eliminate, causes of lung cancer and prevent future generations from developing the disease.
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