The present invention demonstrated that soluble fibrin binds to both Mac-1 and ICAM-1-expressing cells and inhibited adherence of these cells and immune cytotoxicity, thus inducing immune suppression in cancer. Additionally, the present invention also demonstrated that soluble fibrin enhanced metastasis in an in vivo model. Furthermore, the present invention demonstrated the utility of specific peptides that block binding of soluble fibrin to these cells as therapeutic agents in cancer progression and metastasis. It is further contemplated that these peptides can also be used to treat other diseases such as cardiovascular disease, arthritis and in many inflammatory responses where there is increased levels of soluble fibrin.