The present invention is directed to compositions and methods for inhibiting the development of new lymphatic vessels, and for inhibiting tumor cell dissemination through the lymphatics. In preferred embodiments, the present invention utilizes agents that inhibit the specific binding of integrin alpha4beta1 (α4β1, VLA-4) to one or more of its ligands. The invention further relates to methods for screening test compounds for their ability to inhibit undesirable lymphangiogenesis and/or tumor metastasis.