Nelipepimut-S (formerly known as E75) is an immunogenic peptide from the HER2 protein that is highly expressed in breast cancer. The NeuVax™ (Galena, OR, USA) vaccine, nelipepimut-S plus granulocyte-macrophage colony-stimulating factor, is designed for the prevention of clinical recurrences in high risk, disease-free breast cancer patients. Nelipepimut-S is being developed by Sellas Life Sciences Group. When combined with the immunoadjuvant granulocyte-macrophage colony-stimulating factor (GM-CSF), nelipepimut-S has been used as a vaccine that is capable of eliciting a robust anti-HER2 immune response. Early-phase clinical trials that enrolled women with node-positive or high-risk node-negative breast cancer who had been rendered disease free with standard of care therapy but were at risk for recurrence, demonstrated the vaccine to be safe with a suggestion of clinical benefit. Nelipepimut-S is currently being evaluated in a Phase III clinical trial.