A cancer priming vaccine consisting of tumor-specific shared neoantigens, which are immunogenic and unique across a subset of patients, with potential immunostimulating and antineoplastic activities. Upon administration of neoantigen-based therapeutic cancer vaccine GRT-C903, followed by the boosting vaccine GRT-R904, the peptides stimulate the host immune system to mount a specific cytotoxic T-lymphocyte (CTL) response against the shared neoantigens expressed on tumor cells, which results in tumor cell lysis.