Background: After initial pancreatic resection, local recurrence of pancreatic cancer (PC) or new primary PC can develop in the remnant. There are limited data available regarding this so-called remnant PC. The aim of this retrospective study was to clarify the clinical features and establish a treatment strategy for remnant PC. Methods: A multicenter retrospective study with the Kyushu Study Group of Clinical Cancer was carried out. Clinical data from 50 patients who developed remnant PC were analyzed. RAS mutation analysis of the initial tumor and of remnant PC was performed in 17 cases. Results: The initial pancreatic resections were performed for 37 invasive ductal carcinomas, and for 13 other tumors. Thirty-seven patients underwent a second pancreatectomy for remnant PC (resected group), while thirteen patients were not operated (unresected group). The median overall survival times were 42.2 months in the resected group and 12.3 months in the unresected group (HR 0.374; 95% CI 0.17–0.83). In RAS mutation analysis, 14 cases had at least 1 missense variant of KRAS, HRAS, or NRAS in the initial pancreatic tumor and/or remnant PC. The same missense variants between the initial tumor and remnant PC were discovered only in KRAS of one patient, and in HRAS of one patient. No case had completely consistent missense variants between the initial tumor and remnant PC. Conclusions: This study found that repeated pancreatectomy for remnant PC can prolong patient survival, and RAS mutation analysis indicated that many remnant PCs are developed from metachronous multifocal origins.
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