Evolving neoplasms accumulate non-synonymous mutations at a high rate, potentially enabling the expression of antigenic epitopes that can be recognized by the immune system. Since they are not covered by central tolerance, such tumor neoantigens (TNAs) should be under robust immune control as they surge. However, genetic defects that impair cancer cell eradication by the immune system coupled with the establishment of local immunosuppression can enable TNA accumulation, which is generally associated with improved clinical sensitivity to various immunotherapies. Here, we explore how tumor-intrinsic factors and immunological processes shape the mutational and antigenic landscape of evolving neoplasms to influence clinical responses to immunotherapy, and propose strategies to achieve robust immunological control of the disease despite disabled immunosurveillance.