Aim. The objective is to compare the differences on prognosis and the therapeutic benefits between initial and second primary\ncolorectal cancer (pCRC). Methods.Adataset containing 377,271 initial pCRCcases and 18,617 second pCRCcases fromtheNational\nCancer Instituteâ??s Surveillance, Epidemiology, and End Results (SEER) 1988â??2015 was evaluated. Survival comparisons were made\nusing the log-rank test. Cox proportional hazards models were used to assess the survival benefits. Results. The cancer-specific\nsurvival rate of patients with initial pCRC was significantly higher than that of patients with second pCRC (5-years survival rate:\n64.85% vs. 60.22%, P<0.001). The Chi-square of stratified log rank for age at diagnosis was lower than that for primary site, pTNM\nstage, sex, race, histology, and grade (Chi-square=86.73). Therewere almost no differences on therapeutic benefits between patients\nwith initial and second pCRC except that treatments with chemotherapy were significantly associated with longer survival rate\ncompared with treatments without chemotherapy among stage III surgical initial and second primary left-sided colon cancers patients (HR=0.764 vs. 0.581; P for interacti Conclusion. Patients with second pCRC have worse prognosis than those\nwith initial pCRC primarily because of older age in the former group. The results evidenced that the therapeutic benefits on the\nprognosis for colorectal cancer were generally similar between patients with initial and second pCRC.
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