Reaching Metastases in the Brain

Metastasis is one of the most frightening words in the cancer lexicon. It describes the spread of cancer cells beyond the organ where a cancer originated, and once it begins, the disease becomes much harder to treat. About 1 in 5 of all people with cancer develop metastases in the brain — an especially difficult situation that can lead to serious cognitive problems and can be fatal.1,2

Treating these metastases can be difficult because the brain is protected by a sophisticated membrane called the blood-brain barrier. This barrier is an important protective measure, but it also does not allow most medicines to enter. Recently, however, a better understanding of how the blood-brain barrier works has led to the development of targeted treatments that can pass through it and treat cancer both where it started and in the brain.

Cancer cells can travel to the brain through the bloodstream or lymphatic system.3 Lung cancer is the most common source of brain metastases.

Specialized cells within the blood-brain barrier screen potentially harmful substances, such as neurotoxic compounds and pathogens, out of the blood as it passes into the brain from the rest of the body.4 This barrier is so selective that 98 percent of all medicines cannot pass through.5

The barrier lets select molecules into the brain through a variety of mechanisms, including dissolving them in the membrane and transporting them across it through pores or in cellular containers called vesicles. As scientists learn more, they are developing medicines that can commandeer these mechanisms to enter the brain and reach tumors. Often these novel treatments are targeted therapies, which recognize tumor-specific proteins and are designed to treat the underlying drivers of that type of cancer.6,7