Twenty years after testing an experimental breast cancer vaccine, all study participants are still alive, a remarkable result in metastatic disease[2]. The researchers found that the participants' immune systems retained long-lasting memory cells capable of recognizing cancer cells[2]. Researchers have identified a key immune signal called CD27, which by boosting dramatically improved tumor elimination in laboratory experiments[2]. During the study's ten-year follow-up, 80% of treated participants were still alive, significantly higher than the expected 50% of patients with advanced HER2 breast cancer[2]. The findings suggest that cancer vaccines may have been missing this key component of the immune system all along[2]. The results were recently published in the journal JAMA Oncology[2].