The primary sites leading to brain metastases: Shifting trends at a tertiary care center

While the majority of brain metastases arise from lung cancer, breast cancer, or melanoma, new treatments and improved prognoses have altered the profile of primary cancers that metastasize to the brain. We sought to determine the proportion of brain metastases from less common primary sites and conduct trend analyses. We reviewed the charts of 3585 patients with brain metastases seen at our institution from 2008 to 2018. We determined the primary site for each of these patients, and the Mann-Kendall test was used to evaluate temporal trends in the yearly proportion of brain metastases originating from each primary cancer. The five most common primary sites were lung (43.0%), breast (19.9%), melanoma (8.2%), renal (5.0%), and colorectal (3.8%). The proportion of yearly brain metastases originating from breast cancer (p = 0.029) and melanoma (p = 0.013) decreased by 23.8% and 46.7%, respectively, from 2008 (0.21 breast, 0.15 melanoma) to 2018 (0.16 breast, 0.08 melanoma), while no change was found in the proportion of brain metastases from lung, renal, and colorectal cancers. Brain metastases arising from rare primary sites, defined as those comprising at most 2% of all brain metastases, increased by 34.4% (p = 0.005). Limited sample size prohibited trend analysis of other individual primary sites. We report a decrease over 11 years in the proportion of brain metastases originating from breast cancer and melanoma at our institution, and an increase in brain metastases from rare primary sites. Further work with larger, multi-center databases will enable additional evaluation of brain metastases from rare primary sites.