Immunohistochemical staining of vasopressin receptors. V2R expression was detected using polyclonal antibodies against the human receptor, as described in detail in “Patients and methods”. Representative pictures of tumor sections from patients enrolled in the trial and positive control tissue are depicted. a Breast carcinoma expressing V2R b V2R-negative breast carcinoma c Kidney tubules d MCF-7 human breast carcinoma xenograft. Arrowhead denotes positive staining of small vessels. Original magnification: a, b, d ×400; c ×100.