Background: Surgical resection is the only potentially curative treatment for pancreatic ductal adenocarcinoma (PDAC). However, most of patients lose the chance of surgery due to the unresectable disease at the time of diagnosis. Despite the improvement of radiological imaging, a portion of patients intended for radical resection were proven to be unresectable at surgical exploration due to occult metastasis.Methods: Patients who were aimed to undergo radical pancreatectomy for PDAC from 2010 to 2019 were reviewed retrospectively. All patients included underwent diagnostic laparoscopic exploration. Patients were divided into two groups depending on whether distant metastasis were encountered during exploration.Univariate and multivariate logistic regression analyses were used to identify risk factors for occult metastasis.A nomogram to predict occult metastasis of PDAC on exploration was developed and evaluated.Results: A total of 273 patients who underwent diagnostic laparoscopic exploration were included in this study. Nineteen (7.0%) patients were found with distant metastasis during exploration. Multivariate logistic regression analysis showed that ALT>40U/L, CA19-9, CA125 and regional nodes enlargement were independent predictors for occult metastasis. Incorporating these four factors, the nomogram achieved concordance index of 0.799, with a well-fitted calibration curve.Conclusions: Occult metastasis is not unusual during surgical exploration in patients with resectable or borderline resectable PDAC. The nomogram could achieve a personal prediction of unexpected distant metastasis on exploration. It may help to sift through patients with PDAC who would benefit from laparoscopic exploration.

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