Abstract 5291: Effect of screening CT results and features on lung cancer risk prediction within the National Lung Screening Trial
Authors: Robbins Hilary A. , Berg Christine D. , Cheung Li C. , Chaturvedi Anil K. , Katki Hormuzd A. 
Published: July 2017

Abstract
BACKGROUND: In the course of screening, individual risk of disease evolves based on screening results. We calculated how individual lung cancer risk changes based on screening CT findings using data from the National Lung Screening Trial (NLST), which conducted annual screening for 3 years.
METHODS: We calculated lung cancer risks by combining CT findings with individual predicted 1-year “pre-screening risk.” Pre-screening risk r(x) was predicted in the absence of screening using a validated risk model (Katki et al., JAMA 2016) with covariates (x): age, education, sex, race, smoking intensity/duration/quit-years, body mass index, family history of lung cancer, and self-reported emphysema. We used log-binomial regression to calculate the risk of an “interval” lung cancer (within 1 year of a negative screen) or a “screen-detected” cancer detected at the next annual screen. For each, covariates included log-transformed 1-year pre-screening risk and CT findings including classification as negative or false-positive and other specific features.
RESULTS: The median 1-year pre-screening risk at the first NLST screen was 0.32% (interquartile range 0.19-0.53%). Among CT-negatives, risk over the next year was substantially reduced as r(x)1.32 (median interval cancer risk 0.05%), but risk at the next screen reverted to pre-screening risk as r(x)1. Risk at the next screen was higher for those whose CT noted either emphysema (r(x)0.95, median risk 0.53%) or consolidation (r(x)0.76, median risk 1.6%).
Among CT-false-positives, overall risk at the next screen increased as r(x)0.74 (median risk 1.5%). Risk was higher among those with nodule(s) that were larger, had spiculated margins (median risk 4.1%), were located in the upper lobes (median risk 1.4%), or grew during the most recent screening interval (median risk 7.9%), while nodules with smooth margins indicated lower risk (median risk 0.71%). Those with a smooth-margins nodule and no risk-increasing factors essentially reverted to their pre-screening risk at the next screen as r(x)1.01 (median risk 0.29%), as if they had screened negative. Overall, only the immediately prior screen result, and not earlier screens, predicted lung cancer risk (all p&gt;0.2). Exponents were similar for each interval and at each screen (all p&gt;0.07).
CONCLUSIONS: CT-negatives experienced reduced lung cancer risk over the next year, but reverted to their pre-screening risk at the next screen. CT-false-positives experienced substantially increased lung cancer detection at the next annual screen, with most risks exceeding 1%. These risk increases were explained by specific CT features including nodule size, location, margins, and growth.
Citation Format: Hilary A. Robbins, Christine D. Berg, Li C. Cheung, Anil K. Chaturvedi, Hormuzd A. Katki. Effect of screening CT results and features on lung cancer risk prediction within the National Lung Screening Trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5291. doi:10.1158/1538-7445.AM2017-5291