Once cancer has spread to different organs, it is known as metastatic cancer. Cancer that has spread into the brain is known as brain metastases. These most commonly develop in patients with skin, lung and breast cancer and are observed in ~30% of all patients with metastatic cancer.

Over the past decade, a new therapy known as immunotherapy has been approved for the treatment of metastatic cancer. Immunotherapy blocks specific molecules that are present on a subpopulation of white blood cells, and this helps the immune system to attack cancer. Immunotherapy significantly extends lives of some patients with metastatic skin cancer. However, there are many patients in which the current immunotherapy doesn’t work. Therefore, our goal is to develop improved immunotherapy approaches that can inhibit metastatic cancer in a larger population of patients. To achieve this, we first need to gain a better understanding of how the immunotherapy and immune system in general work within brain metastases. Analysis of brain metastases tissue isolated from patients that received immunotherapy, and comparison to therapy-naïve tissue, will help us to understand this and enable us to develop improved immunotherapy approaches.