brain metastasis
Meaning of brain metastasis: Cancer in the brain has far more often arrived from elsewhere than started there, and that origin decides how it is treated.
Definition of brain metastasis
A brain metastasis is a deposit of cancer inside the brain that grew from a tumor which started somewhere else, most often the lung, breast, skin or kidney. The cells travel through the bloodstream, lodge in small vessels and grow there. Under the microscope they still look like the original cancer, so a deposit from a breast tumor remains breast cancer.
How does it differ from a tumor that starts in the brain?
By origin, and the difference is not academic. A brain tumor arising from brain tissue is made of brain cells gone wrong. A metastasis is made of cells from the organ where the cancer began, so its appearance under the microscope, its behavior and the drugs it responds to all follow that first site. Spread deposits also tend to be multiple, round and clearly edged, while tumors starting in the brain more often form a single mass with an ill-defined border.
Which cancers reach the brain?
| Cancer of origin | Pattern |
|---|---|
| Lung | The commonest source overall |
| Breast | Certain subtypes reach the brain more readily |
| Melanoma | Strong tendency for its frequency, often several deposits |
| Kidney and bowel | Less common, more often a single deposit |
Why do symptoms appear?
The skull cannot expand, so anything growing inside it competes for space. Swelling in the tissue around a deposit often causes more trouble than the deposit itself. Headache, weakness on one side, clumsiness, changed speech, seizures or a shift in personality follow from where the growth sits rather than from what it is made of, which is why the first sign can be mistaken for a stroke.
Why is treatment different from treating the same cancer elsewhere?
The blood brain barrier keeps most large molecules out of brain tissue, so a drug controlling disease in the chest may do little for a deposit in the brain. Treatment therefore leans on surgery and on focused radiation aimed at each deposit, with steroids used to settle the swelling around it. Some newer drugs are designed to cross into the brain, which has changed the picture for particular tumor types.
Also known as
Used in a sentence
Imaging showed a solitary brain metastasis in the right frontal lobe.
Good to know
A deposit in the brain keeps the identity of the cancer it came from, so the tissue of origin rather than the location decides which drugs are considered.
Word origin
Where “brain metastasis” comes from
Metastasis comes from the Greek meta, meaning beyond or changed, with stasis, meaning a standing, giving the sense of a change of place.