The impact of a prior malignancy on outcomes in gastric cancer patients

BACKGROUND: The number of cancer survivors has increased rapidly, and there is a higher risk of developing a second cancer. Whether a prior malignancy could affect survival outcomes is unknown. We aimed to investigate the clinical characteristics and prognostic outcomes of prior malignancies in patients with gastric cancer. METHODS: Patient data were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. We used the Kaplan–Meier method, competing risk models, and Cox regression models to evaluate the impact of prior malignancy on survival outcomes. RESULTS: Among 71,809 patients with primary gastric cancer, 6667 (9.3%) patients had a pre‐existing cancer. Prostate (31.86%), breast (14.34%), and colon and rectum (10.32%) cancer were the most common types. A significant difference was observed in the overall survival rates between patients with and without prior cancer (log‐rank=139.73, p < 0.001). In the subgroup analysis, patients with prostate, uterine corpus, lung and bronchus, colon and rectum, esophagus, urinary bladder, leukemia, brain and other nervous system, oral cavity and pharynx, and breast cancer faced inferior survival than those without prior cancer. CONCLUSIONS: A history of prior cancer was associated with worse overall survival in patients with gastric cancer, and the effects varied by different initial cancer types. The exclusion and inclusion of patients who had previous malignancies should be reconsidered according to the specific malignancy types.