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A Possible Definition of Oligometastasis in Pancreatic Cancer and Associated Survival Outcomes

Background: Oligometastatic cancer (OM) is possibly associated with relatively better survival outcomes. We attempted to identify cases in line with this OM concept. Patients and Methods: A total of 130 cases with unresectable metastatic pancreatic cancer underwent non-curative surgery from April 2001 to December 2019. Sites of metastasis, clinicopathological information, and surgical outcomes were collected to formulate a better definition of OM. Results: OM criteria were defined as having metastasis to a single organ, few countable lesions and low serum cancer antigen 19-9 level. The median overall survival after non-curative surgery of OM cases was 13.0 months and was significantly better than that of non-OM cases (8.4 months, p=0.003). Conclusion: We propose single-organ metastasis of limited tumor volume (H1 or P1/2 by the Japanese Society of Cancer of the Colon and Rectum classification) and low serum cancer antigen 19-9 level (<2,000 U/ml) as new criteria for defining OM pancreatic cancer.