A replication incompetent adenoviral vector encoding the full-length tumor suppressor gene Reduced Expression in Immortalized Cells (REIC or DKK3) (ad-REIC/DKK3), with potential antineoplastic activity. Upon intratumoral injection, tumor cells express REIC/DKK3 protein. This may result in the activation of c-Jun-NH2-kinase (JNK) and ultimately apoptosis via Bcl2 suppression and caspase-3 activation. Expression of REIC/DKK3 is normal in healthy cells but reduced or absent in many cancer cells; Forced overexpression of REIC/DKK3 in cancer cells may lead to an induction of tumor cell apoptosis and reduction of tumor cell growth while sparing normal, healthy cells naturally expressing endogenous REIC/DKK3.