This is a Phase 1, open-labeled, non-randomized, multi-center, competitive enrollment and dose-escalation study of ALT-801, the study drug. The purpose of this study is to evaluate the safety, determine the maximum-tolerated dose (MTD) and characterize the pharmacokinetic profile of ALT-801 in previously treated patients with progressive metastatic malignancies. ALT-801, a recombinant fusion protein with a interleukin-2 (IL-2) component, has a targeting mechanism that recognizes tumor cells with a specific tumor marker.