Thus, an Ig Id can be conceived and used as an antigen to induce anti-Id responses in two different frameworks: (i) the Id itself as a target antigen on tumor cells, as in the case of B cell lymphomas (Figure 2A), and (ii) the Id as a mimic of a tumor antigen, with the anti-Id response ultimately intended to target the latter (Figures 2B,C). This evidence concerns the gene ID1 and neoplasm.