There is disclosed a peptide suitable for eliciting an immune response. The peptide corresponds to a fragment of the RAS protein, and comprises a region of 8 amino acids which includes a mutated position of the RAS protein. Said region has at least 6 amino acid residues, other than the mutated position, which are identical to the corresponding region of the RAS protein. The peptide has apoint mutation at the amino acid corresponding to the mutated position, and the mutated position is position 146 or 117 of the RAS protein.
