This research proposal seeks information about the mechanism(s) for fibrin deposition in cancer. Such information is critical for the design of treatment regimens aimed at this host defense mechanism. The proposal focuses on developing an understanding of the relative importance of tumor-associated procoagulants (PCA) and macrophage tissue factor (MO-TF) in this process. There are four specific goals: 1. Identification of antigens related to tissue factor (TF) (TF:RAg), other tumor PCA, and fibrin in human tumors in situ. 2. Identification and molecular characterization of TF (and other PCA) in isolated human tumor cells and tumor-associated MO. 3. Production and characterization of monoclonal antibodies to rabbit TF. 4. Determination of the in vivo effects of TF-specific, monoclonal antibodies on the expression of MO-TF, the deposition of fibrin and tumor growth in a rabbit tumor model. (A)