Figure 3. Representation of tumor suppressor gene therapy model.

(A) For patients with hereditary retinoblastoma, one copy of the mutated or deleted RB gene is inherited from their parents (the first hit). (B) Acquisition of a second hit, a somatic mutation, causes “loss of heterozygosity” and retinoblastoma. (C) Replacement of the mutated or deleted RB with a normal RB cDNA inhibits tumor growth.