Recommendations for broadening eligibility criteria in esophagus cancer clinical trials: the mortality disparity of esophagus cancer as a first or second primary malignancy

Background: Esophagus cancer as a second primary malignancy (esophagus-2) is increasingly common, but its prognosis is poorly understood. This study aims to examine the overall, non-cancer related and cancer-specific survival of patients diagnosed with esophagus-2 compared to the first primary esophagus cancer (esophagus-1). Methods: We included primary esophagus cancer patients diagnosed from 1975 to 2019 in the Surveillance, Epidemiology, and End Results program. Esophagus-2 was identified in patients with a previous diagnosis of non-esophageal primary malignancy. Hazard ratios of overall, esophagus cancer-specific and non-cancer related mortality were estimated among patients with esophagus-2 compared to esophagus-1, adjusting for age, gender, tumor stage and other demographic and clinical characteristics. Results: A total of 74,521 and 14,820 patients were identified as esophagus-1 and esophagus-2 respectively. Esophagus-2 patients suffered lower risk of esophagus cancer-specific mortality in initial 5 years but with similar risk thereafter, independent of tumor characteristics and treatment. In the first 5 years after diagnosis, patients with esophagus-2 had similar risk of overall mortality with those with esophagus-1 but increased risk thereafter. As for non-cancer related mortality, esophagus-2 patients had higher risk all along. Conclusions: Esophagus-2 patients should not be entirely excluded from clinical trial and a 3-year exclusion window is suggested. A conservative approach to manage esophagus-2 solely based on malignancy history is not supported but effort should be put into surveillance, prevention and management of the comorbidities and complications for the first malignancy.