Survival impact of occult liver metastasis and peritoneal dissemination compared with radiologically defined distant organ metastasis in pancreatic ductal adenocarcinoma.

Background: Characteristics and prognoses of patients with occult metastases (OM) of pancreatic ductal adenocarcinoma (PDAC) compared with radiologically defined metastases (RM) have been rarely reported.

Objective: We aimed to clarify the prognosis of OM compared with RM and to establish a treatment strategy for PDAC patients with OM.

Methods: This single-institution, retrospective study evaluated patients with unresectable PDAC between 2008 and 2018. OM was defined as abdominal metastasis that was detected by staging laparoscopy or open laparotomy but not in the initial assessment of radiological images.

Results: OM and RM were identified in 135 and 112 patients, respectively. Eastern Cooperative Oncology Group Performance Status (ECOG PS), neutrophil to lymphocyte ratio (NLR), tumor diameter, and rate of local unresectability were significantly lower in the OM group. Median overall survival (OS) of OM was significantly better than that of RM (13.0 vs 8.9 months, p < 0.001). In multivariate analysis of OS, ECOG PS ≥ 1 (HR 1.64, p = 0.009), NLR ≥5 (HR 1.97, p = 0.004), carbohydrate antigen (CA) 19-9 ≥1000 (HR 1.68, p = 0.001), tumor diameter ≥40 mm (HR 1.40, p = 0.027), conversion surgery (HR 0.12, p < 0.001), and multiple lines of chemotherapy (HR 0.38, p < 0.001) were independent predictors. However, type of metastasis (OM vs RM) not an independent predictor (HR 1.10, p = 0.590).

Conclusion: The prognosis of PDAC with OM was relatively better than that with RM, but general and nutritional statuses, primary tumor size and CA19-9, conversion surgery and multiple lines of chemotherapy were independent predictors but not tumor burden.