Proposal for a definition of "Oligometastatic disease in pancreatic cancer".

Background: To date, patients with metastasized pancreatic ductal adenocarcinoma (PDAC M1) are regarded as a uniform collective. We hypothesize the existence of oligometastatic disease (OMD): a state of PDAC M1 disease with better tumor biology, limited metastasis, and increased survival.

Methods: Data of 128 PDAC M1 patients treated at the University of Cologne between 2008 and 2018 was reviewed. Interdependence between clinical parameter was calculated using the Mann-Whitney U-Test. Survival curves were generated using the Kaplan-Meier method and analyzed using the log-rank test.

Results: Eighty-one (63%) patients had metastases confined to one organ (single organ metastasis, SOG) whereas the remaining 47 (37%) showed multiple metastatic sites (multi-organ metastasis, MOG). Survival analysis revealed a median overall survival (OS) of 12.2 months for SOG vs 4.5 months for MOG (95% CI 5.7-9.8; p < 0.001). We defined limited disease by the presence of ≤4 metastases in liver or lung. Limited disease together with CA 19-9 baseline < 1000 U/ml and response or stable disease after first-line chemotherapy defined OMD. We identified 8 patients with hepatic metastases and 2 with pulmonary metastases matching all OMD criteria. This group of 10 (7.8%) had a median overall survival of 19.4 vs 7.2 months compared to the remaining patients (95% CI 5.7-9.8; p = 0.009).

Conclusion: We propose a definition of oligometastatic disease in PDAC including anatomical criteria and biological criteria reflecting better tumor biology. The 10 OMD patients (7.8%) survived significantly longer and might even benefit from surgical resection in the future.