The majority patients diagnosed with pancreatic cancer have metastatic disease at the time of diagnosis. The prognosis is extremely poor with a 5-year survival rate of less than 5%. Treatment with chemotherapy can improve efficacy, but still the median progression-free survival in patients receiving nab-paclitaxel and gemcitabine is only 5,5 months and median overall survival is less than one year. There is a urgent need for tools for predicting the efficacy of the treatment. The current trial aims at investigating the biomarker potential of circulating tumor cells (CTCs) in metastatic pancreatic cancer patients treated by gemcitabine and nab-paclitaxel.