Trends in research on indoor radon exposure and lung cancer in South Korea.

Editorial Radon is recognized by the World Health Organization as a lung cancer-causing carcinogen in humans, and is the second most common cause of lung cancer after smoking [1]. A causal relationship between radon and lung cancer was first described in epidemiological studies on underground mine workers. Thereafter, case–control studies further demonstrated that exposure to low concentrations of radon carries a risk for lung cancer. Recently, pooling studies have set out to investigate lung cancer risk in relation to exposure to radon indoors. In South Korea, a total of 47,869 men died from cancer in 2014, comprising 32.5 % of all male deaths that year. Among these Korean men, lung cancer had the highest mortality rate, compared to all other cancer types, and accounted for 12,785 deaths, corresponding to 26.7 % of all deaths from cancer. Meanwhile, in the same year, a total of 28,742 women died from cancer in South Korea, comprising 23.9 % of all deaths among women. As in men, lung cancer exhibited the highest mortality rate, accounting for 4655 deaths (16.2 % of all deaths from cancer) [2]. As the incidence of lung cancer has continued to increase, studies have been undertaken to outline the etiology thereof. Histologically, lung cancer is primarily classified into small cell lung cancers (about 20 % of all lung cancers) and non-small cell lung cancers (80 %); non-small cell lung cancer is further subdivided into adenocarcinoma (40 %), squamous cell carcinoma (30 %), and large cell carcinoma (15 %). Small cell lung cancer is typically malignant, and in most cases, metastasizes to other organs before it is detected. Generally, smoking is considered to be the main cause of lung cancer: small cell lung cancers and squamous cell carcinoma are positively associated with smoking, whereas adenocarcinoma exhibits relatively lower correlation with smoking [2–4]. Meanwhile, however, 10–25 % of all cases of lung cancer are not directly related to smoking [5]. Reports suggest that passive smoking increases the risk of lung cancer by 35 % in men and 25 % in women [6]. Lung cancer has also been found to be related with radon exposure, exposure to potential lung carcinogens (asbestos, polycyclic hydrocarbons, silica, heavy metals, etc.), oil vapor when cooking, coal combustion, hormonal factors, and air pollution [7]. Despite awareness of radon’s association with lung cancer, Koreans are less aware of the potential risks of indoor radon exposure. This paper aimed to review trends in studies on indoor radon exposure and lung cancer in South Korea, to suggest the need to establish reference levels for indoor radon levels specific to South Korea, and to highlight the necessity of continuous indoor radon exposure-related research. In this article, we outline eight papers published on indoor radon exposure and lung cancer with respect to Korea, covering topics related to epidemiological studies, mathematical-statistical modeling, environmental burden of disease, genetics biomarkers, and radon measurement methods. The following summarizes our findings from reviewing research on indoor radon exposure: