Breast cancer vaccine. Molecular model showing the secondary structure of alpha-lactalbumin. This molecule has been successfully used as a vaccine against breast cancer in mice bred to be prone to the disease. The vaccine primes the body's immune system to attack tumour cells that display the alpha-lactalbumin molecule (thought to be between 50% to 70% of breast cancers). The vaccine was successful at preventing tumours as well as at stopping tumour growth in mice that had already developed breast cancer.