The present invention provides immunoassays for detecting a tumor in a subject, comprising producing an antibody that specifically binds to tenascin, contacting the antibody with a biological sample suspected of containing tumor cells and determining the binding of the antibody to the biological sample. The present invention further provides methods of identifying a subject for treatment of a tumor. Kits for direct or indirect immunohistochemical or immunocytochemical assays are also provided. A novel polyclonal antibody that binds to tenascin domain TNfn C-D is further provided.