# Indoor Air Pollution Increases the Risk of Lung Cancer
## 4 Discussion
conducted a study on temple workers and found a significant increase in DNA damage; they observed a 2-fold increase in the levels of leukocyte 8-hydroxy-2'-deoxyguanosine (8-OHdG) and DNA strand breaks (\(p\) < 0.001) [40]. In Taiwan, [PERSON] et al. assessed human exposure to airborne PM and PAHs during heavy incense burning episodes in temples. The study calculated a 50% probability of exceeding the DNA adduct frequency (DA(f)) ratio for external exposure of Benzo(a)Pyrene and Benzo(a)Pyrene(eq) and a 10% probability of lung tumor due to internal exposure of Benzo(a)Pyrene and Benzo(a)Pyrene(eq). These results implicate that exposure to smoke emitted from mass incense burning may increase lung cancer risk [41]. Since incense burning is a tradition in Chinese culture, we suggest that the public and temple workers should improve ventilation when they burn incense. Traffic might be an essential source of PAHs in the air [42]. In the Nurses' Health Study from the United States, the researchers used residential distance to major roadways as a proxy for traffic-related exposure. The study indicated that an increased risk of lung cancer was associated with ambient traffic-related PM exposure, especially among never- and long-term former smokers [43]. Studies in Europe and Canada also used the distance to a main roadway or traffic intensity as a proxy for traffic-related exposure to assess the risk of lung cancer. The results showed that traffic-related air pollution contributed to an increased risk of lung cancer [44; 45; 46; 47; 44]. In this study, we compared the distances between home and the main street and did not find a significant difference between the case group and the control group. The study subjects came from Taipei City. We conducted a pilot study to measure the respiratory effect of urban air pollution on cyclists in November and December 2017. We selected a bike lane from a major road and parallel small streets along the major road. The distance of each route was 5 km. Study subjects were randomly allotted to the major road route (\(n\) = 3) and a small street route (\(n\) = 3) and node their bicycles for one hour. With the continuous measurement of the concentration of PM\({}_{2.5}\) by DustTrak, the mean levels of PM\({}_{2.5}\) of the high-traffic route and low-traffic route were 7.12 and 5.09 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\), respectively. The traffic-related air pollutants in Taipei are not severe compared with other cities. We conservatively estimate that traffic-source air pollution might not be responsible for the increased risk in our case group. Due to the development of mass spectrometry techniques in environmental analysis, exposure data are often nonlinear, and many variables are highly correlated. The selection of a cluster from the pool of all potential clusters may cause the \"Texas sharpshooter phenomenon,\" which is a term used to refer to post hoc studies: the Texas sharpshooter shoots first, then draws the target where most bullets have hit [48]. To choose the most influential chemical from multiple chemicals from GC-MS analysis, we applied the machine learning technique to model multiple exposures data that are highly correlated. In Taiwan, lung cancer is the leading cause of cancer-related death, and the majority of patients (84.1%) are diagnosed in advanced stages (stage III and stage IV) [49]. Therefore, the majority of lung cancer patients enrolled in this study were in an advanced stage, which might have introduced recall bias since lung cancer patients were likely to recall more exposure history. Recall bias might also exist in the family history of lung cancer. The prevalence of first-degree relatives ever having lung cancer was much higher in the case group than in the control group. The ORs of habitual cooking and burning incense at home might be overestimated. The etiology of pneumonia, heart failure, pneumothorax, ischemic bowel disease, and Sjogren's syndrome are not associated with air pollution.