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.