The invention relates generally to the screening of candidate molecules for the treatment of tumor metastasis, and treatment methods using such molecules. Thus, the invention includes a method of screening comprising the steps of: (1) administering a plurality of test substances to a non-human syngeneic immunocompetent animal model bearing at least one soft tissue or bone metastasis, in the presence or absence of a primary tumor; (2) determining the effects of the test substances on the soft tissue or bone metastasis and growth of the primary tumor, if present; and (3) identifying a test substance that inhibits the growth of a soft tissue or bone metastasis, without adverse effect on the status of the primary tumor, if present.