Incidental pulmonary nodules, lung cancer screening, and lung cancer in the Medicare population.

6536 Background: Low-dose CT lung cancer screening (LDCT) saves lives, but only 5%-10% of eligible persons in the US have participated. Management of indeterminate pulmonary nodules (IPNs) identified on CT scans may also reduce lung cancer mortality. We assessed the frequency of IPNs, estimated cumulative lung cancer rates following IPNs, and compared characteristics of lung cancers diagnosed following IPNs versus LDCT screens. Methods: We defined 2 cohorts in the SEER-Medicare database: persons with 12+ months of Medicare Part A&B coverage during 2014-2019 comprised the 5% sample cohort; persons in SEER-Medicare diagnosed with lung cancer during 2015-2017 with Part A&B coverage for the prior 18-month period comprised the lung cancer cohort. We defined IPNs as chest CTs with ICD-10 codes of R91.1 (solitary pulmonary nodule) or R91.8 (other nonspecific abnormal finding of lung field) on the same date as the CT; we used corresponding ICD-9 codes through September 2015. We classified lung cancer cohort cases by whether they had an LDCT (LDCT group), an IPN without an LDCT screen (IPN-only), or neither (Referent) within 18 months before diagnosis. We compared cancer stage and survival between these groups. Results: Of 627,547 subjects in the 5% sample cohort, 58.6% were women; 85.6% were non-Hispanic White (NH-Whites) and 7.7% non-Hispanic Black (NH-Blacks). Over median 5.0 years follow-up, 26.3% had chest CTs and 12.0% had IPNs. The IPN rate was similar by sex but significantly higher in NH-Whites (12.7%) than NH-Blacks (9.7%). The cumulative lung cancer rate following initial IPNs was 2.27% at two years. Of the 44,194 lung cancer cohort cases (85.8% NH-White, 8.2% NH-Black), 26.9%, 2.9% and 70.2% were in the IPN-only, LDCT, and Referent groups, respectively. NH-Whites comprised a higher proportion of LDCT than of IPN-only cases (90.1% vs. 88.4%), while for NH-Blacks, the reverse was true (5.4% vs. 6.5%). The ratio of LDCT:IPN lung cancer cases was 1:9. Among IPN-only and LDCT group cases, 52.0% and 50.3%, respectively, were localized stage, compared to 21.5% for the Referent group. Among all localized cases, 45.4% and 4.9% were in the IPN-only and LDCT groups, respectively. Comparing 3-year survival between IPN vs LDCT vs Referent groups, respectively: aggregate overall survival rates were 53.5% v 59.2% v 29.2%; aggregate lung cancer-specific survival, 71.1% v 75.3% v 46.6%; overall survival for localized cases, 73.2% v 80.7% v 62.9%; lung cancer-specific survival rates for localized cases, 88.2%, 91.8% and 81.4%. Conclusions: Subjects with IPNs had similar stage distribution and survival as LDCT-screened subjects. Almost half of localized cases had prior IPNs, compared to a < 5% of LDCT-screened cases. IPN programs, by circumventing implementation barriers to LDCT, may expand access to early lung cancer detection, including to African American patients and in places where LDCT coverage is not available.