Featured Researcher—Susan Murin, M.D., MsC
Dr. Susan Murin
is Associate Professor of Clinical Internal Medicine at the University
of California, Davis.
Smoking Effect on Pulmonary Metastasis from Breast Cancer
Breast cancer patients who smoke are more likely to die from the disease than non-smoking breast cancer patients. Susan Murin of the University of California, Davis, provides direct, experimental evidence that exposure to cigarette smoke is associated with an increase in the spread of cancer cells to the lung. Read more >
Ask an Expert
If you’d like to ask Dr. Murin a question about her research, please email your question to susanMurin@cabreastcancer.org any time between October 16 and November 30. New questions and answers will be posted regularly, so check back for updates.
Dr. Murin adds:
The limitations of the types of experiments and analyses we and others have done to explore the relationship between smoking and breast cancer spread (metastasis) or death from breast cancer need to be kept in mind. It has been observed that smoking women with breast cancer are more likely to die than non-smoking women. The studies that have made this observation can not definitely determine a cause and effect relationship between smoking and these worse outcomes. There is a bit of a leap between observing that two things are associated and concluding that one causes the other.
We know that smokers tend to be different from non-smokers in other ways (for example, on average their diets are less healthy, they have menopause earlier, and they may be from lower socioeconomic groups and have less access to health care), so it is very hard to sort out which things might be the cause of the worse outcomes. That is why we did experiments in mice, in order to see if one of the reasons for worse outcomes might be that smoking made it more likely that breast cancer would spread to the lung. Mice and other animals are commonly used to try and answer medical questions for many reasons, one of which is that you can change one thing at a time (like smoke exposure) while keeping everything else (like diet) the same. However, there are certainly limitations to animal experiments and thus to the conclusions that can be drawn from them about human diseases.
- Q: Is there a level of smoking that triggers the metastasis? (e.g., a
pack a day vs. one cigarette per day)
A. In our mouse experiments it looked like there was what is called a ‘dose-response’ relationship between smoke exposure and increasing metastasis, meaning that the higher the level of exposure the higher the risk, but this wasn’t certain. With most smoking-related diseases, the higher the level of smoking, the higher the level of complications. There is not considered to be any ‘safe level’ of smoke exposure, but certainly the lower the better.
- Q: Will second-hand smoke affect metastasis?
A. We don’t know the answer to this question, and likely never will, as it is simply too hard to study. Second-hand smoke has been shown to have a variety of ill-effects, so there are plenty of other reasons to avoid it!
- Q: How much is your model for metastasis representative of what happens
in humans?
A. This animal model is commonly used to study breast cancer but there are certainly differences between humans and mice. These experiments were done using cancer cells derived from a single clone commonly used for such experiments. Human cancers are not as homogenous. Sometimes what happens in mice is very predictive of what happens in humans, sometimes it’s not. The types of experiments we did in the mice could never be done in humans, so we will never know exactly how the results would compare.
- Q: Do menthol cigarettes or other types of tobacco make a difference?
A. We don’t know the answer to this question. However, for other smoking-related diseases (lung cancer, vascular diseases) there is no difference in the risk associated with menthol vs. non-menthol cigarettes- so my educated guess is that it wouldn’t matter.
- Q: How long does it take for the cancer to metastasize when exposed to
cigarette smoke?
A. The types of experiments we and others have done don’t provide enough information to answer this question.
- Q: How about smoking and cancer recurrence? If I quit smoking
after I’m
diagnosed, and continue to not smoke after my treatment, is there any protective
benefit that would continue throughout the rest of my life?
A. Yes, there is very likely to be benefit to quitting after diagnosis. Several studies have shown improved outcomes from a variety of different cancers for those who quit smoking at the time of their cancer diagnosis. Also, some complications of cancer therapy occur more commonly in patients who smoke. So all patients diagnosed with cancer should be strongly encouraged to quit!
For More Information about This Researcher
For other CBCRP-funded research projects by Dr. Murin
For Dr. Murin’s bio (UCD website)
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