Provided herein are pro-VP antagonists, such as antibodies and antigen-binding portions thereof specific for pro-VP, for identifying and targeting expressing cancer cells. Applicants additionally provide methods of using said compositions, for example to image cancer cells in vivo and in biological samples. The compositions may also be used for treating patients suffering from a provasopressin-expressing cancer. Provasopressin-expressing cancers include neuroendocrine cancer, pancreatic cancer, and prostate cancer.
