Proposing the use of hyponatremia as a marker to help identify high risk individuals for lung cancer Pashtoon Murtaza Kasi ⇑ International Scholars Program, Department of Internal Medicine, University of Pittsburgh Medical Center (UPMC), Pittsburgh, PA 15213, USA article info Article history: Received 15 March 2012 Accepted 13 May 2012 abstract The use of computerized tomography (CT) scans has been recently brought into attention to help screen high risk individuals for lung cancer. Even though they are highly sensitive, their cost seems to be the main hindrance. Our hypothesis is to see if other factors could help identify a subset amongst the high risk individuals. Our focus specifically is on hyponatremia. It is well known that patients with lung cancer can have associated hyponatremia and multiple mechanisms have been put forward. Our hypothesis is that the degree of hyponatremia can be correlated with size or aggressiveness of the tumor and if true, then screening high risk individuals with hyponatremia can yield more patients with possible lung can- cer. This, therefore, may help decrease the associated costs as compared to imaging/screening everyone with a CT scan for lung cancer and have a major impact at the public health level. Ó 2012 Elsevier Ltd. All rights reserved. Background Lung cancer and screening ‘Long-term survival is quite uncommon in refractory small cell lung cancer (SCLC) patients, with less than 25% of patients with limited-stage disease and 1–2% of patients with extensive-stage disease remaining alive at 5 years’ [1]. In another series of 114 pa- tients, metastases were present in 49.1% of patients at presentation [2]. Such numbers highlight the need for screening tools that can help catch the disease early. The use of computerized tomography (CT) scans (more specifi- cally the low-dose CT scans) has been recently brought into atten- tion to help screen high risk individuals for lung cancer and also has been shown to decrease mortality [3]. This argument is sup- ported by the fact that routine chest X-rays (CXR) for surveillance purposes cannot catch nodules or tumors till they are much larger in size and identifying lung cancer early in these individuals may help prevent morbidity, mortality and overall healthcare associ- ated costs. On the other hand, CT scans are not a cheap modality. Even though they are highly sensitive as well as specific to an ex- tent, their cost seems to be the main hindrance and the argument put forward by those against the use of routine CT scans for surveillance in these individuals. Insurance agencies currently would not approve the use of CT scans as a surveillance strategy for lung cancer in patients with a significant smoking history. Our hypothesis is to see if other factors could be brought into the equation to further identify a subset amongst the high risk individuals (essentially smokers). The specific factor that that we think may be very useful in helping identify individuals with lung cancer is serum sodium levels/hyponatremia. Hyponatremia and lung cancer Serum sodium levels are very cheap and are essentially part of any basic or comprehensive metabolic panel. It is well known that patients with lung cancer can have associated hyponatremia (more common with small cell lung cancer) [4]. The mechanisms put for- ward for hyponatremia are outlined as follows: (1) Syndrome of Inappropriate Anti Diuretic Hormone secretion (SIADH): either directly from the mass being within the lungs or from ectopic release of ADH from tumor cells. SIADH as noted above is a common paraneoplastic syndrome caused by small cell carcinoma (SCC) [5]. (2) Raised levels of atrial natriuretic peptides (ANPs) through ‘persistent natriuresis and inappropriately low aldosterone levels’ [6,7]. (3) Involvement of adrenal or brain through metastases further contributing to the degree of hyponatremia [8]. Hyponatremia in some case reports has been attributed to other causes as well [9]. 0306-9877/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mehy.2012.05.023 Abbreviations: ANP, atrial natriuretic peptide; CI, confidence interval; CT, computerized tomography; OR, odds ratio; Na+, sodium; NSCLC, non small cell lung cancer; SIADH, syndrome of inappropriate anti diuretic hormone secretion; SCLC, small cell lung cancer. ⇑ Tel.: +1 412 897 2301. E-mail address: pashtoon.kasi@gmail.com Medical Hypotheses 79 (2012) 327–328 Contents lists available at SciVerse ScienceDirect Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy