). A family history of lung cancer is a risk factor for both smokers and those who never smoked, with an overall relative risk in the range of 1.5 that can extend up to 1.8 in patients with an affected sibling. Race is also a factor, with a significantly higher incidence of lung cancer in black men and native Hawaiian men at low levels of smoking when compared with that in white men (74).
Tobacco and Other Inhaled CarcinogensCigarette smoking has been established as the major risk factor for lung cancer since the 1960s, with a 10- to 35-fold increased risk when compared with that in nonsmokers, and exposure to secondhand smoke is a proven, albeit lesser, risk factor (75–77). The association between adenocarcinoma, which accounts for virtually all subsolid lung cancers, and smoking is weaker than the association between small cell or squamous cell carcinomas and smoking, and the incidence of adenocarcinoma in nonsmokers is increasing, with female nonsmokers being affected significantly more often than male nonsmokers (75,77). However, the degree to which smoking affects the risk for lung adenocarcinoma has not been clearly defined; thus, our recommendations for management of subsolid nodules are independent of customary risk categories (78). A smoking history of 30 pack-years or more and quitting smoking within the past 15 years have been used as the qualifying tobacco exposure threshold for the NLST screening program, and they should be considered indicative of high-risk status in patients with solid nodules. Other inhaled carcinogens that are known risk factors for lung cancer include exposure to asbestos, uranium, or radon (79–81). Smokeless electronic cigarettes have been introduced, but possible risks associated with these products are as yet unproven (82). Risk Estimation and Risk ModelsThese guidelines for nodule management are based on estimations of the individual risk of malignancy. Although nodule size and morphology remain the dominant factors that we use to predict risk, it is important to consider additional clinical risk factors, including smoking, exposure to other carcinogens, emphysema, fibrosis, upper lobe location, family history of lung cancer, age, and sex. Because these factors are numerous and have differing effects on the likelihood of cancer, several sophisticated risk prediction models have been developed (Appendix E1 [online]). However, for the purposes of these guidelines, we recommend that risk be assigned according to the categories proposed by the American College of Chest Physicians (ACCP). Low risk, which corresponds to an estimated risk of cancer of less than 5%, is associated with young age, less smoking, smaller nodule size, regular margins, and location in an area other than the upper lobe. To estimate high risk, we recommend combining the ACCP intermediate-risk (5%–65% risk) and high-risk (>65% risk) categories. High-risk factors include older age, heavy smoking, larger nodule size, irregular or spiculated margins, and upper lobe location. Subjects with intermediate risk share both high- and low-risk characteristics (83 |