Alternative splicing of osteopontin (OPN) produces three isoforms: OPNa, OPNb, and OPNc. The aims of this study were to examine the expression profile of OPN isoforms in sera from patients with pancreatic lesions and to determine their correlation with the presence of comorbid systemic inflammatory conditions, such as diabetes and/or obesity. Sera from 90 patients undergoing pancreatic surgery and 29 healthy volunteers were analyzed. Seventeen patients were diabetics, 17 were obese, and 6 had both diabetes and obesity. In patients with pancreatic lesions, OPNb was expressed in 48% of the patients' sera, OPNc in 34%, and both in 5%. The presence of diabetes and/or obesity was associated with complete disappearance of OPNb and expression of only OPNc. OPNc presence was significantly associated with diabetes and obesity (OR = 7.06 [95% CI 1.97-23.3]; p = 0.003). No OPNb or OPNc was detected in the normal sera. Overexpression of OPNb and OPNc isoforms in PDA cells significantly (p < 0.05) increased their activity in soft-agar colony formation and wound healing assays, induced the transcription of interleukin (IL)-6, and reduced tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ), and IL-10. Our data show for the first time the significant association between serum OPNc and diabetes and/or obesity. Unraveling the functional role of OPN isoforms in systemic inflammation is essential to understanding their significance as therapeutic targets in diabetes and obesity, and during metastasis development in PDA.