Prognosis Of Lung Cancer As A Second Primary Malignancy Among Cancer Survivors: A Population-Based Cohort Study.

e21005 Background: Cancer survivors are at increased risk of developing a second primary malignancy, including lung cancer. However, prognosis of lung cancer as a second primary malignancy (lung-2) remains largely unknown. This study aims to investigate the prognosis of lung-2 in relevant to lung cancer as a first primary malignancy (lung-1). Methods: Lung cancer patients from 1988 to 2014 in the Surveillance, Epidemiology, and End Results program were included. Overall and lung cancer specific mortality are the main outcome. Second primary malignancy was defined according to SEER rules. Results: 679,541 and 85,758 patients were included as lung-1 and lung-2 in this study, respectively. The median time from first primary malignancy to lung-2 diagnosis is 4.3 years. Compared to lung-1, patients with lung-2 were more likely to be diagnosed at localized stage, with smaller primary tumor, and treated with surgery. Lung-2 was associated with favorable overall (HR 0.97, 95% CI 0.96-0.98) and lung-cancer specific (HR 0.80, 95% CI 0.79-0.80) mortality compared to lung-1. The favorable overall survival of lung-2 was primarily contributed by the decreased risk of overall mortality within first year after cancer diagnosis. The risk of lung cancer specific mortality was reduced within the first 5 years after diagnosis. Conclusions: Lung-2 is not more aggressive compared to lung-1 and is not associated with inferior cancer-specific survival. Table 1 Mortality risk of lung cancer as a second primary malignancy Lung cancer as a first primary Lung cancer as a second primary HR HR (95% CI) Overall mortality Model A* 1.00 0.86 (0.85-0.87) Model B† 1.00 0.97 (0.96-0.98) Lung cancer specific mortality Model A* 1.00 0.70 (0.69-0.70) Model B† 1.00 0.80 (0.79-0.80) HR, hazard ratio; CI, confidence interval* Model A: Adjusted for age and calendar period at diagnosis, sex, race, cohabitation status, and percentile of high-school education, household income in county of residence. †Model B: Adjusted for tumor stage, histology, tumor grade, surgery, radiation therapy, and chemotherapy in addition to what are included in model A.