1. A high risk of incident lung cancer exists for smokers that do not meet low-dose computed tomography screening criteria.

2. Early cessation of smoking results in a lower risk of incident lung cancer.

Evidence Rating Level: 1 (Excellent)

Study Rundown: The United States lung cancer screening guidelines recommend adults between 50 and 80 years old with a minimum 20 pack-year history of smoking who continue to smoke or who have quit within the last 15 years receive low-dose computed tomography (LDCT). This cohort study aimed to determine lung cancer risk in older adults who smoke, but do not meet the guideline criteria. The primary outcome of interest was lung cancer incidence during a median follow-up period of 13.3 years (7.9-18.8 years). Of participants who had never smoked, 0.5% developed lung cancer. In participants who smoked less than 20 pack years, 5.0% of current smokers, 1.6% of those who quit 15 or more years ago, and 1.4% of those who quit less than 15 years ago developed lung cancer. In participants with 20 or more pack years of smoking history, 16.2% of current smokers, 5.0% of those who quit 15 or more years ago, and 10.1% of those who quit less than 15 years ago developed lung cancer. Limitations to this study include the possibility of smoking category cross-over during follow-up, under-reporting of cigarette use by participants, and the ages of the participants (65 years or older) may limit the generalizability to a younger population. Overall, the results from this study provide evidence of a high risk of lung cancer in smokers that do not meet the LDCT screening criteria.

Click to read the study in JAMA Oncology

Relevant Reading: US Preventive Services Task Force. Screening for lung cancer: US Preventive Services Task Force recommendation statement

In-Depth [systematic review and meta-analysis]: This prospective cohort study included 4,279 participants from the Cardiovascular Health Study data sets. These participants were grouped into 7 categories based both on years of smoking cessation and pack-years. The categories were “never smokers” (1973 participants), “nonheavy smokers” with less than 20 pack years smoking history (861 total participants), and “heavy smokers” with 20 or more pack-year smoking history (1445 total participants). These nonheavy smokers included former smokers who quit 15 or more years ago (615 participants), those who quit less than 15 years ago (146), and current smokers (100). Heavy smokers included former smokers who quit 15 or more years ago (516), those who quit less than 15 years ago (497), and current smokers (432). In never smokers, 10 people (0.5%) developed lung cancer. For former nonheavy smokers who quit 15 or more years ago, 10 people (1.6%) developed lung cancer. In those who had quit less than 15 years ago, 2 (1.4%) developed lung cancer. In current nonheavy smokers, 5 people (5.0%) developed lung cancer. In former heavy smokers who had quit 15 or more years ago, 26 people (5.0%) developed lung cancer. 70 current heavy smokers (16.2%) and 50 former heavy smokers who quit less than 15 years ago (10.1%) developed lung cancer. The hazard ratio (HR) for incident lung cancer for nonheavy smokers who quit 15 or more years ago was 3.22 (95% confidence interval (CI), 1.34-7.73), 2.64 (95% CI, 0.58-12.04) for those who quit less than 15 years ago, and 10.54 (95% CI, 3.60-30.83) for current heavy smokers compared to never smokers. The HR for heavy smokers who quit 15 or more years ago was 11.19 (95% CI, 5.40-23.21), 23.51 (95% CI, 11.92-43.36) for those who quit less than 15 years ago, and 39.29 (95% CI, 20.24-76.25) for current heavy smokers compared to never smokers. This study indicates that there are high risk patients that are not captured in the current guidelines representing patients who are former smokers who do not return to baseline despite many years of smoking cessation, highlighting the importance of screening in this population.

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