CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) are understood to maintain peripheral tolerance to self-antigens and inhibit antitumor immune responses. However, compelling evidence suggests that, Tregs provide no anti-inflammatory protection in the tumor microenvironment, but rather contribute to a T helper 17 (Th17)-driven pro-carcinogenic process. Using three-color flow cytometry, we evaluated the percentage of circulating CD4(+)CD25(+)FoxP3(+) Tregs in the peripheral blood of pancreatic carcinoma patients prior to and after chemotherapy [gemcitabine (GEM) alone, or GEM+oxaliplatin (GEMOX) or bevacizumab+capecitabine+radiotherapy (BEV+CAPE+RT)]. Correlations were sought between Treg counts and plasma levels of cytokines relevant to controlling the Treg/Th17 balance, i.e., interleukin (IL)-23, IL-17A, IL-6 and transforming growth factor β 1 (TGF-β1), as measured by ELISA and the clinical features of pancreatic cancer. Treg, IL-6 and TGF-β1 levels were higher in locally advanced and metastatic pancreatic carcinoma patients compared to controls. No parameter was correlated with disease stage except IL-6. IL-17A and TGF-β1 were significantly associated with increased risk of poor prognosis. IL-17A was positively correlated with IL-23. Treg and IL-6 levels decreased following GEM monochemotherapy, IL-17A levels decreased after GEMOX, and IL-6 levels were reduced subsequent to BEV+CAPE+RT treatment. IL-23, IL-17A and TGF-β1 levels were significantly lower in patients responding to chemotherapy (partial remission/stable disease) than in nonresponders to chemotherapy (progressive disease). These results suggest an impact of the Treg/Th17-balance in pancreatic carcinoma, highlighting the significance of TGF-β1 and IL-17A as potential prognostic and predictive indicators. Immunological changes induced by mono and/or combined chemotherapy indicate specific windows of opportunity for introducing integrative interventions on a new target in pancreatic cancer, i.e. IL-17A, possibly improving survival in this highly lethal disease.