A Possible Definition of Oligometastases in Pancreatic Cancers and Their Survival Outcomes

Abstract Background: Among advanced metastatic cancers, oligometastatic cancers (OM) are defined as having limited visible metastases, possibly associated with relatively better survival outcomes. We attempted to identify cases that are in line with the concept of OM among unresectable metastatic pancreatic cancer, using a retrospective cohort.Methods: A total of 130 cases with unresectable metastatic pancreatic cancer received non-curative surgery (palliative surgery or staging laparotomy) from April 2001 to December 2019. Metastatic sites, clinicopathological information, and surgical outcomes were collected to reveal definition of OM.Results: Primary tumor sites were pancreatic head in 80 cases and others in 50 cases. Performed operations were gastrointestinal tract bypass in 68 cases and staging laparotomy in 62 cases. Based on the survival outcome differences, OM criteria were defined as single organ metastasis, a few countable lesions (4 or fewer organ metastases or limited peritoneal metastases) and low serum CA19-9 level (< 2000 U/ml). The median overall survival time (MST) after non-curative surgery of OM cases (n=54) was 13.0 months and was significantly better than non-OM cases (n=76) (MST:8.4months, 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 CA19-9 (< 2000 U/ml) as a new criteria for OM.