An estimated 70,000 diagnoses of brain metastases (BM) occur each year in the U.S., with an incidence of 5-7% in breast and melanoma and 20% in lung cancer. Despite its prominence, the biology of BM remains poorly understood. Several theories of BM development exist,
including the linear progression model, which suggests that the metastatic capabilities of tumor cells develop at primary sites following the accumulation of alterations. The parallel progression model argues that tumor cells disseminate early and accumulate changes independently at the secondary site. We compare the tumor profiles of BM from common cancers to understand the biology and to identify differential treatment strategies.