The genetic variations observed in most advanced cancers decrease the effectiveness of many anti-cancer agents through the development of drug resistance. Therefore, alternative approaches to the direct targeting of cancer cells are urgently needed. Bavituximab is the generic name for a chimeric (human/murine) monoclonal antibody directed against aminophospholipids. Bavituximab is Peregrine's first investigational product under its anti-phospholipid therapy technology platform. Anti-phospholipid therapy is a novel approach to treating cancer. It is based on the finding that aminophospholipids, which are basic components of the inner surface of cells become externally exposed in response to certain disease states such as cancer. Laboratory and animal studies have demonstrated that bavituximab specifically targets cancer cells and inhibits tumor growth in a variety of experimental cancer models. This study will examine the safety and tolerability of bavituximab when administered to patients with advanced solid tumor cancers that are unresponsive to current therapies. Cohorts of 6 patients each will be treated at the starting dose of 0.1 mg bavituximab per kilogram body weight (0.1 mg/kg). Successive patient cohorts will receive 0.3, 1.0 and 3.0 mg/kg of bavituximab. Patients will be followed for a total of 56 days. Patients who demonstrate an objective tumor response will be offered further bavituximab treatment on an extension protocol.