Cancer’s spread to brain isn’t random, study says. Some types target certain regions

Sometimes, cancer forms in one part of the body and later spreads to the brain in a condition called brain metastasis. Scientists have always thought this process to be random, meaning cancer cells set up shop wherever they land in the brain, but new research suggests there’s more organization to the deadly chaos.

Researchers from the University of Southern California analyzed more than 3,100 brain tumors that originated from cancers in the skin, lung, breast, kidney or colon of 973 patients treated at the Keck Medical Center from 1994 to 2015.

They learned the region where cancer spreads in the brain is dependent on where the cancer first appeared in the body. Lung and skin (melanoma) cancers are more likely to spread to the brain’s frontal and temporal lobes that sit behind the ears, while breast, kidney and colon cancers have a higher likelihood of spreading to the back of the brain where the cerebellum and brainstem are located.

The study also showed people with colon and breast cancers were more likely to have larger brain tumor volumes than people with skin cancer.

The findings helped researchers develop two models that confirmed brain metastasis has “distinct geographic spread” depending on its origin. The models could one day help doctors predict where someone’s cancer may spread and help stop it; they could also deepen researchers’ understanding of how brain tumors grow.

“If we can understand what factors either facilitate or block the process of metastasis, such as certain chemicals or neurotransmitters in the brain, there might be a way to intervene and prevent a cancer from metastasizing in the first place or treat it once it has spread,” study lead author Dr. Josh Neman, an assistant professor of neurological surgery and physiology and neuroscience at USC’s Keck School of Medicine, said in a news release posted Thursday.

“In fact, we are already conducting studies to learn why certain areas of the brain are not receptive to certain cancer cells in hopes of developing better targeted therapies for patients,” Neman said.

Data used in the study came from patients with metastatic brain cancer who underwent stereotactic radiosurgery, a minimally invasive procedure that allows surgeons to identify tumors’ specific coordinates and beam the masses with X-rays from the outside to block the growth of cancerous cells. The procedure reduces the likelihood of patients developing cognitive issues compared to those who have their entire brain exposed to radiation.

Neman speculates that cancer cells may have the ability to adapt to specific parts of the brain that “allow them to colonize and progress, while other areas of the brain are inhospitable to the same cells.”

“Microenvironments” that cater to cancer cells’ needs are referred to as “metastatic niches,” the study notes, like how humid kitchens are prime breeding grounds for mold.

Where tumors grow in the brain can also determine what symptoms people could experience. For example, patients with breast or colon cancer whose tumor spreads to their brainstem may have difficulty speaking and swallowing, have droopy eyelids or have muscle weakness on one side of their body. Patients with skin or lung cancer whose tumor spreads to their frontal or temporal lobes may experience impaired judgment, loss of smell or vision, increased aggressive behavior or memory problems.

The study was published in July in the Journal of Neurosurgery.