It has been noted for many years that Asian women appear to be particularly predisposed to lung cancer despite a low frequency of smoking. Many of the series from resected NSCLC series have never-smoker rates of 30-50%, with the majority of these never-smokers as women. As we’ve struggled to understand and explain risks, hormonal differences between men and women have emerged as a possibility, as has genetic differences. One other idea that has been the subject of several studies is that exposure to fumes from cooking oils at a high heat, such as wok cooking, may expose Asian never-smoking women to a mutagenic toxin that could explain some of the high incidence of lung cancer among Asian never-smokers.
Several aspects of cooking may be relevant, including the method, such as deep frying vs. stir frying, as well as the question of whether fume extractors were present, and the number of years that a person has been cooking and therefore potentially exposed. There are also many limitations to these studies, because they tend to be retrospective reviews of patients with lung cancer that are compared to prior exposure of similar patients (age, sex, socioeconomic status, etc.), called a case-control study. There is a risk of recall bias, in which someone now with lung cancer is likely more likely to remember some remote exposure to a potential toxin than a random happy and health person now challenged to think of some prior exposure to some questionable toxin. Also, because this is an observational study of outcomes for real people interacting in many complex ways, there could be confounding variables that make it possible that some variable not related directly to cooking but potentially traveling with exposure to cooking fumes — perhaps exposure to toxic dishwasher detergent (I doubt it, but who knows?).
One interesting study, for instance, looked at exposures of 672 Chinese women with lung cancer (among whom 65% were never-smokers) compared with 735 control women without lung cancer (abstract here). Although there were many factors that could be relevant, including a history of TB or other lung diseases, and also late menopause, there was a considerably higher risk of lung cancer associated with exposure to cooking with high heat cooking oil; rapeseed oil was identified in particular, and it is used at a high heat that can produce toxic fumes (abstract here). Stir frying 30 or more dishes per week was also associated with a 2.6 higher risk of developing lung cancer than in people who did not stir fry frequently. In fact, other case-control studies have also identified cooking oils as a risk , particularly in Chinese women (abstracts here and here).
It’s not really possible to measure exposure to toxic fumes from cooking, and something like this is definitely subject to recall bias. In Seattle, I see a rather large proportion of Asian never-smoking women with lung cancer. A few have stood out in my mind as supporting the role of cooking fumes — young women who have worked as wok cooks, or otherwise in a restaurant — but this only applies to perhaps a couple of the 60-80 Asian never-smoking women with lung cancer I’ve treated over the last 5 years. It may be a component, but I doubt it provides a major explanation for most of the cases of lung cancer in never-smoking women, Asian or of other races. However, if you are a never-smoker with lung cancer and have a significant exposure to high heat cooking oils, please leave a comment. It may be a more common direct link than I’ve been able to discern.
posted by Dr. West @ 11:26 pm link to this post
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November 28th, 2007 at 12:13 pm
My mom was recently diagnosed with NSCLC. She fits in the group of a Chinese never-smoker and did 99% of the cooking when we were growing up. I would say the majority of the cooking was not high heat wok cooking, but there was quite a lot of stir frying. Although I’m certain my mom’s cancer developed from exposure to prolonged high levels of radon, the cooking oils may have been a factor as well. My mom is pretty petite/short, and therefore her face is closer to the cooking food…perhaps proximity to the cooking food results in greater inhalation of the unhealthy fumes?
November 29th, 2007 at 9:20 am
Perhaps, but I’ve never seen a correlation with height in such analyses (not sure how much it’s been looked at, but some of these studies did evaluate a huge number of variables).
I had been thinking of doing a post on radon and lung cancer risk, so you’ve given me one more reason to get on that.
-Dr. West
November 30th, 2007 at 10:14 am
Thanks Dr. West for these recent posts to explore the ‘Why Am I Sick With Cancer’ question. It takes a lot of research on your part to put these posts together and thanks again for your efforts.
Until the paths to progression of cancer are discovered, hopefully more early detection and diagnosis methods will be developed. The recent passage of Prop. 15 in Texas (supported by the Lance Armstrong Foundation) will bring $2.5 billion in research to developed early detection and diagnosis techniques for more types of cancer including lung cancer. They are looking for research partners now, maybe you?
In the 25 years that we were together, my wife Lisa (Thai, NSCLC never smoker) didn’t do that much wok cooking. If any cooking was done involving smoke and smells, it was always done outside and never indoors so there was plenty of ventalation. Rapeseed oil (high erucic acid) was never used but she did use Canola oil (very low erucic acid) which is from the same family of plants.
Could something 25 years prior to my recall have cause gene hit damage?
One of my theories is that it takes many hits of gene damage to cause progression that the immune system can’t happen. One of these hits could be exposure to incense smoke used in some Asian traditions on a regular basis. Usually incense is burned in a closed environment such as a temple or home.
Another theory is backed up by the recent identification of Duke University scientists of the ’silenced genes’; an important step in studying how our environment - food, stress, pollution - interacts with genes to help determine why some people get sick and others do not.
Stress and how we handled it is high on my list of theories.
Thanks Again - Chanwit
November 30th, 2007 at 8:14 pm
Chanwit,
In most cases, cancer is caused by an accumulation of mutations over many years, which is why it is associated most typically with more advanced age. Never-smokers tend to have a more genetically simple cancer, which is probably why if you hit them right, like with an EGFR inhibitor like tarceva for an EGFR-driven cancer (more common in never-smokers).
I don’t know much yet about the Duke “silenced gene” work, but I’ll try to learn what I can.
I don’t know any information on incense smoke, but it sounds like it could be a possibility. However, we’re seeing lots and lots of cancer among younger asians in the US who don’t share much with more traditional Asian cultures other than genetics. I suspect it’s more genetically driven, but I’d have to admit that we’re early in learning about all of this. What I can tell you is that there has never been more interest in the drivers of cancer, and never more ability to get answers to our questions. I’d bet that our treatments in 5 years will be more individualized, and we’ll have a better understanding of what’s driving the cancer in many people.
Unfortunately, I can’t say that any of us knows this today.
-Dr. West
December 3rd, 2007 at 8:54 am
My wife, Chinese nonsmoker, was 51 in 2004 when diagnosed with nsclc (adenocarcinoma). She cooked regularly for at least 24 years. She frequently did stir-frys but little wok cooking. To the best of my knowledge, the only oil she ever used was olive oil. After coming here in 1984 she was rarely exposed to second-hand smoke.
To complicate matters, she remembered very frequent and heavy second-hand smoke exposure between 1980 and 1984 when she lived in Paris.
I’ll also add that she ate a very healthy diet and exercised regularly, and at the time of her diagnosis, was very healthly. She was also a very small woman.
Bill