Health Sciences Research, Mayo Foundation, Rochester, MN 55905
We thank Dr. Kabir (1) for his interest in our report on the differential association of anthropometric factors with histologic types of lung cancer in the Iowa Womens Health Study cohort (2). We agree that the results from this cohort of older women may not apply to other population groups that include men and younger women. Hopefully, other researchers with the relevant data will be motivated to investigate whether the differential associations of body mass index and waist circumference with lung cancer subtypes seen in our study are observed in other groups.
Dr. Kabirs hypothesis that unmeasured environmental tobacco smoke may explain our results is intriguing but seems somewhat unlikely. Environmental tobacco smoke is certainly an established risk factor for cancer. However, in order for environmental tobacco smoke to act as a confounder to the anthropometric-histologic subtype association, it would have to be associated with both lung cancer (which it is) and waist circumference. We are unaware of any data that suggest that environmental tobacco smoke alone is sufficient to influence fat distribution patterns. If other groups have data on both environmental tobacco smoke and anthropometric factors, including waist circumference, this would be a most intriguing question to address.
In our analyses, we found that increasing quintiles of waist circumference were associated with decreased risk of squamous and small cell lung cancer. However, there was no association seen with waist circumference levels and adenocarcinoma of the lung. As we stated in our article, this was in direct opposition to our a priori hypothesis that adenocarcinoma was the histologic subtype most likely to be influenced by non-tobacco-related causes and would be the type most strongly associated with various anthropometric factors. Further, our results do not support the hypothesis that the current obesity epidemic can explain any portion of the increasing rates of adenocarcinoma being seen today (3, 4). Therefore, in response to Dr. Kabirs "wondering" as to whether our original hypothesis is "always true," our data clearly show that indeed it is not.
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