The present disclosure provides recombinant antigen-binding regions and antibodies and functional fragments containing such antigen-binding regions that are specific for MST1R, which plays an integral role in various disorders or conditions, such as cancer. These antibodies, accordingly, can be used to treat these and other disorders and conditions. Antibodies of the disclosure also can be used in the diagnostics field, as well as for further investigating the role of MST1R in the progression of disorders associated with tumors. The disclosure also provides nucleic acid sequences encoding the foregoing antibodies, vectors containing the same, pharmaceutical compositions and kits with instructions for use.