Brain metastases characteristically localize to which of the following regions?

• A. Lung
• B. Breast
• C. Gray-white matter junction
• D. Meninges

Answer: (C)

Metastatic cancer in the brain most often spreads through the bloodstream and gets trapped where small end-arterioles transition from gray matter to white matter. The gray–white matter junction presents an abrupt change in vessel caliber, making it a prime site for embolic tumor cells to lodge and establish lesions. That’s why brain metastases characteristically appear at this junction, frequently in the cerebral hemispheres.

The other options don’t describe this pattern. The lungs and breasts are common primary sources of brain metastases, but they’re about where the cancer starts, not where it localizes within the brain. Involvement of the meninges indicates leptomeningeal carcinomatosis, a diffuse pattern rather than focal parenchymal metastases.