Given that we entitled our, seemingly controversial, ed- itorial as âCOPD and .... Karoor V, Le M, Merrick D, Fagan KA, Dempsey EC, Miller YE. Alveolar hypoxia ...
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regular recertification like that of the American Board of Internal Medicine (http://www.abim.org/) is not required to continue to practice internal and/or specialty medicine. This is of concern, considering that many in the current medical community may not be adequately trained to face the epochal epidemic of chronic diseases, which requires a comprehensive medical approach. Given that we entitled our, seemingly controversial, editorial as “COPD and the solar system,” let us conclude this response respectfully within the same “astronomical” framework and suggest that physicians around the world should “look at the moon, not just at the finger indicating the moon,” that is, look at the patient with COPD, not just at his or her lung function!
Alvar Agustí, M.D. Thorax Institute, Hospital Clinic, University of Barcelona Barcelona, Spain References 1. Fabbri LM, Beghé B, Agustí A. COPD and the solar system: introducing the chronic obstructive pulmonary disease comorbidome [editorial]. Am J Respir Crit Care Med 2012;186:117–119. 2. Divo M, Cote C, de Torres JP, Casanova C, Marin JM, Pinto-Plata V, Zulueta J, Cabrera C, Zagaceta J, Hunninghake G, et al. Comorbidities and risk of mortality in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2012;186:155–161. 3. Barnett K, Mercer SW, Norbury M, Watt G, Wyke S, Guthrie B. Epidemiology of multimorbidity and implications for health care, research, and medical education: a cross-sectional study. Lancet 2012;380:37–43. 4. Ferrucci L, Studenski S. Clinical problems of aging. Chapter 72. In: Harrison’s principles of internal medicine. 18th Edition. McGraw Hill, New York, 2012. 5. Vestbo J, Hurd SS, Agusti AG, Jones PW, Vogelmeier C, Anzueto A, Barnes PJ, Fabbri LM, Martinez FJ, Nishimura M, et al. Global strategy for the diagnosis, management and prevention of chronic obstructive pulmonary disease, GOLD executive summary. Am J Respir Crit Care Med (In press) 6. Laurin C, Moullec G, Bacon SL, Lavoie KL. Impact of anxiety and depression on chronic obstructive pulmonary disease exacerbation risk. Am J Respir Crit Care Med 2012;185:918–923. Copyright ª 2013 by the American Thoracic Society
Reply: Part of the Whole From the Authors:
We thank Dr. Cerveri and colleagues for their interest in our article entitled “Comorbidities and risk of mortality in patients with chronic obstructive pulmonary disease” (1). We believe the main argument is directed to the editorial by Dr. Fabri and colleagues (2); however, we support the value of measuring pulmonary function in patients with chronic obstructive pulmonary disease (COPD) as an intrinsic element for diagnosis, treatment, and prognosis. We also have demonstrated that COPD goes beyond obstruction; therefore, we support a multidimensional yet simple approach by adding the other elements of the BODE index, the degree of hyperinflation (3), and frequency of exacerbations (4), but don’t forget those comorbidities that influence survival that are included in the COTE index. As a matter of fact, in Figure 3 of our manuscript, we demonstrate how survival is impacted within each BODE category but also how comorbidities modify the survival probability. We endorse the concept of personalized medicine, where patients are evaluated by measuring their physiologic
2013
variables (obstruction and exercise capacity), their symptoms (dyspnea perception in the Medical Research Council questionnaire), and systemic manifestation (expressed by the body mass index) and also by identifying and comanaging existent comorbidities. We have to be integrative rather than reductionist. Author disclosures are available with the text of this letter at www.atsjournals.org.
Miguel J. Divo, M.D. Brigham and Women’s Hospital Boston, Massachusetts and Harvard Medical School Boston, Massachusetts
Author disclosures are available with the text of this letter at www.atsjournals.org.
Leonardo M. Fabbri, M.D. Bianca Beghè, M.D. University of Modena and Reggio Emilia Modena, Italy
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On Behalf of All Authors References 1. Divo M, Cote C, de Torres JP, Casanova C, Marin JM, Pinto-Plata V, Zulueta J, Cabrera C, Zagaceta J, Hunninghake G, et al. Comorbidities and risk of mortality in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2012;186:155–161. 2. Fabbri LM, Beghé B, Agustí A. COPD and the solar system: introducing the chronic obstructive pulmonary disease comorbidome [editorial]. Am J Respir Crit Care Med 2012;186:117–119. 3. Casanova C, Cote C, de Torres JP, Aguirre-Jaime A, Marin JM, PintoPlata V, Celli BR. Inspiratory-to-total lung capacity ratio predicts mortality in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2005;171:591–597. 4. Soler-Cataluna JJ, Martinez-Garcia MA, Roman Sanchez P, Salcedo E, Navarro M, Ochando R. Severe acute exacerbations and mortality in patients with chronic obstructive pulmonary disease. Thorax 2005;60:925–931. Copyright ª 2013 by the American Thoracic Society
Sleep-disordered Breathing, Hypoxemia, and Cancer Mortality To the Editor:
We read the report of increased cancer mortality in the Wisconsin Sleep Cohort Study and accompanying editorial with considerable interest (1, 2). Overall cancer mortality increased in a dose-dependent fashion with severity of sleep-disordered breathing, most strongly with hypoxemia index. The novelty of the findings reported by Nieto and colleagues is in the potential association of cancer mortality with alveolar hypoxia and systemic hypoxemia, as opposed to hypoxia within poorly vascularized tumor regions, which has been extensively studied. As the authors note, the cohort size precluded any analysis of specific tumor types, and limitations in the clinical data available prevent understanding whether increased cancer mortality is a reflection of increased cancer incidence or accelerated tumor progression, invasion, and metastasis. Hypoxia within tumors has been found to be associated with increased levels of hypoxia inducible factor (HIF)-1a, HIF-2a, various angiogenic factors, and worse patient outcomes, as recently reviewed (3). Paradoxically, areas within the lung itself can be particularly hypoxic, either due to parenchymal lung disease or as a result of apnea. We have recently reported that exposure of mice to hypobaric hypoxia simulating 18,000 ft elevation with a reduction in PaO2 to 35 to 40 mm Hg causes significantly (two- to threefold) increased lung tumor volumes in two chemical carcinogenesis models (4). We performed these studies to determine whether the existence of hypoxic regions of lung might explain part of the increased lung cancer incidence in chronic obstructive pulmonary disease (5). These changes were accompanied by upregulation of HIF-2a and c-Myc but not HIF-1a, as well as increased proliferation, angiogenesis, angiogenic factors and
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their receptors, antiapoptotic proteins, mitogen-activated protein kinase signaling and proteins associated with epithelial to mesenchymal transition. As might be predicted, these tumors were more sensitive to a vascular endothelial growth factor receptor/epidermal growth factor receptor tyrosine kinase inhibitor given as chemoprevention. Similar experiments modeling the intermittent hypoxia seen in sleep-disordered breathing did not result in increases in tumor volume, HIF-2a, and c-Myc expression or the other changes seen in continuous hypoxia. Although these findings are somewhat at odds with the report of Nieto and colleagues as well as the solitary melanoma flank xenograft model they cite (6), we believe that this only emphasizes the need for further investigation of the interaction between alveolar hypoxia, systemic hypoxemia, and cancer biology, on both the preclinical and clinical levels. Important questions include the relationship of these to specific cancer sites, especially lung, and the roles of continuous or intermittent hypoxia, as well as severity of hypoxemia. Author disclosures are available with the text of this letter at www.atsjournals.org.
York E. Miller, M.D. Vijaya Karoor, Ph.D. Edward C. Dempsey, M.D. Denver Veterans Affairs Medical Center Denver, Colorado and University of Colorado Denver Aurora, Colorado Karen A. Fagan, M.D. University of South Alabama Mobile, Alabama References 1. Nieto FJ, Peppard PE, Young T, Finn L, Hla KM, Farre R. Sleepdisordered breathing and cancer mortality: results from the Wisconsin Sleep Cohort Study. Am J Respir Crit Care Med 2012;186:190–194. 2. Redline S, Quan SF. Sleep apnea: a common mechanism for the deadly triad–cardiovascular disease, diabetes, and cancer? [editorial]. Am J Respir Crit Care Med 2012;186:123–124. 3. Shimoda LA, Semenza GL. HIF and the lung: role of hypoxia-inducible factors in pulmonary development and disease. Am J Respir Crit Care Med 2011;183:152–156. 4. Karoor V, Le M, Merrick D, Fagan KA, Dempsey EC, Miller YE. Alveolar hypoxia promotes murine lung tumor growth through a VEGFR-2/EGFRdependent mechanism. Cancer Prev Res (Phila) 2012;5:1061–1071. 5. de Torres JP, Marín JM, Casanova C, Cote C, Carrizo S, Cordoba-Lanus E, Baz-Dávila R, Zulueta JJ, Aguirre-Jaime A, Saetta M, et al. Lung cancer in patients with chronic obstructive pulmonary disease: incidence and predicting factors. Am J Respir Crit Care Med 2011;184:913–919. 6. Almendros I, Montserrat JM, Ramirez J, Torres M, Duran-Cantolla J, Navajas D, Farre R. Intermittent hypoxia enhances cancer progression in a mouse model of sleep apnoea. Eur Respir J 2012;39:215–217.
growth in mice (3, 4). In their murine model, Almendros and colleagues tried to closely mimic human sleep apnea by placing mice in boxes subjected to 60 hypoxic events per hour, consisting of 20 seconds at 5% O2 concentration followed by 40-second periods of normal room air. In contrast, Miller and colleagues’ model consisted of subjecting mice to alternating 2-minute periods of hypoxia (10% O2 concentration) and normoxia (2). The difference in the experimental approaches might be part of the explanation for the discrepancy in the findings from these studies. Alternatively, it might be that the cancer growth promotion effect of intermittent hypoxia is cancer site/type–specific, that is, relevant in certain tumors (e.g., melanoma) but not in others (e.g., lung cancer). Our prospective cohort study in the Wisconsin Sleep Cohort was not designed or powered to examine the association between SDB (and one of its defining features—intermittent hypoxia) and mortality from specific cancers. Our a priori hypothesis was that intermittent hypoxia increases progression of all cancers—or at least that of solid cancers, through either systemic or local (within-tumor) effects. It is also conceivable that neither Almendros and colleagues’ nor Miller and colleagues’ murine models have direct relevance to our results. It might be that the association we found is due to SDB increasing the risk of cancer incidence rather than cancer progression. It is also possible that SDB affects carcinogenesis and/or cancer progression primarily via mechanisms other than direct effects of intermittent hypoxia. SDB—via pathways that may, but do not necessarily, involve intermittent hypoxia—promotes the formation of reactive oxygen species and induces oxidative stress, inflammation, and altered immune function (5), which in turn might promote carcinogenesis or tumor progression (6, 7). These alternative explanations notwithstanding, our results do meet traditional guidelines supporting a causal relationship (8): biological plausibility, consistency with other evidence (murine melanoma cancer growth model), temporality (findings from a prospective study), dose–response, and strength of the associations. Furthermore, the fact that the association was stronger when the hypoxemia index was used to define SDB (a 8.6 relative hazard associated with severe SDB) than when the apnea–hypopnea index was used (a corresponding 4.8 relative hazard) supports the hypothesis that hypoxemia may be one, if not the primary, pathogenetic mechanism. In any event, and in agreement with the editorial that accompanied our article (9), we believe that our findings emphasize once more the notion that SDB may affect fundamental physiologic functions with potentially significant health consequences. We wholeheartedly agree with Miller and colleagues in their conclusion that more research is needed to elucidate the possible implication of SDB as a causative factor in cancer incidence or mortality. Author disclosures are available with the text of this letter at www.atsjournals.org.
F. Javier Nieto, M.D., Ph.D. Paul E. Peppard, Ph.D. Laurel Finn, M.S. Khin Mae Hla, M.D., Ph.D. Terry Young, Ph.D. University of Wisconsin Madison, Wisconsin
Published 2013 by the American Thoracic Society
Reply From the Authors:
We thank Miller and colleagues for their interest in our article reporting an association between sleep-disordered breathing (SDB) and cancer mortality (1). In their commentary, Miller and colleagues discuss our results in the context of their own experimental work showing that, in contrast with chronic hypoxia, intermittent hypoxia was not associated with increased lung tumor growth in mice (2). Our study was inspired by Almendros and coworkers’ findings that experimental intermittent hypoxia increases melanoma tumor
Ramon Farré, Ph.D. Universidad de Barcelona Barcelona, Spain References 1. Nieto FJ, Peppard PE, Young T, Finn L, Hla KM, Farré R. Sleepdisordered breathing and cancer mortality: results from the Wisconsin Sleep Cohort Study. Am J Respir Crit Care Med 2012;186:190–194.
