Primary CNS Lymphoma, from the CureRays guide library.

Primary CNS lymphoma is a lymphoma that begins in the brain, spinal cord, or eyes; it is treated mainly with specialized chemotherapy that reaches the brain, with radiation used in selected situations.

What it is.

Primary central nervous system (CNS) lymphoma is an uncommon, aggressive lymphoma — a cancer of immune system cells — that begins in and stays confined to the central nervous system: the brain, spinal cord, the membranes covering them, and the eyes. Although it is a lymphoma rather than a typical brain tumor, it grows within the brain and is treated very differently from cancers like glioblastoma. Most cases are a subtype called diffuse large B-cell lymphoma. Symptoms come from where the lymphoma sits in the brain and may include changes in thinking or memory, personality or behavior changes, weakness or numbness, trouble with balance or speech, headaches, or vision problems if the eyes are involved. The disease is more common in older adults and in people whose immune systems are weakened. Because the brain is protected by a natural barrier that keeps many drugs out, ordinary lymphoma chemotherapy does not work well; instead, treatment centers on special high-dose chemotherapy (built around a drug called methotrexate) that can cross into the brain. Radiation, which the disease is very sensitive to, was once a mainstay but is now used more selectively — for example, to consolidate a chemotherapy response, when chemotherapy cannot be given, or to relieve symptoms — because of concerns about long-term effects on thinking, especially in older patients. Care is coordinated by a team of neuro-oncologists, hematologist-oncologists, and radiation oncologists.

How radiation treats it.

Radiation uses focused high-energy beams to damage the DNA inside cancer cells so they can no longer grow and divide. Primary CNS lymphoma is very sensitive to radiation, which is why radiation was historically a mainstay and remains a powerful tool. Because the lymphoma tends to spread microscopically through the brain rather than staying in one spot, radiation is usually directed at the whole brain rather than a single area. The challenge is that radiation to the whole brain — especially at the higher doses used in the past — can affect memory and thinking over time, particularly in older adults, who make up many patients with this disease. For that reason, modern treatment leads with high-dose chemotherapy that crosses into the brain, and uses radiation more selectively: as consolidation after chemotherapy (often at a reduced dose to protect cognition), when chemotherapy cannot be given safely, to treat the eyes when they are involved, or to relieve symptoms quickly. Advanced planning techniques can also spare memory-related regions of the brain. Treatment is given as a series of short daily sessions, and the dose and target are tailored to the goal of care and the patient's age and overall health. Your radiation and neuro-oncology team will balance the strong effectiveness of radiation against protecting long-term brain function.

The ways we can treat it.

Whole-brain radiation therapy. Because the lymphoma can seed throughout the brain microscopically, radiation is often directed to the whole brain rather than a single spot; this controls the disease broadly, and modern practice favors lower doses to reduce effects on memory and thinking.

Reduced-dose consolidation radiation. After chemotherapy achieves a good response, a lower dose of whole-brain radiation can consolidate the remission while limiting the long-term cognitive side effects seen with older, higher-dose radiation.

Radiation to the eyes. When lymphoma involves the eyes, targeted radiation can treat them effectively, either alongside brain treatment or for eye-only disease.

Hippocampal-sparing techniques. Advanced planning can reduce dose to memory-related brain regions during whole-brain radiation, aiming to lower the impact on memory and thinking.

Questions we hear often.

Is this a brain tumor or a lymphoma? It is a lymphoma — a cancer of immune cells — that happens to begin in and stay within the brain, spinal cord, or eyes. That distinction matters, because it is treated very differently from typical brain tumors, relying mainly on special chemotherapy that can reach the brain, with radiation used selectively.

Why isn't radiation always used first if the cancer is so radiation-sensitive? The lymphoma responds strongly to radiation, but whole-brain radiation — especially at older, higher doses — can affect memory and thinking over time, particularly in older adults. Leading with chemotherapy and using radiation more selectively, at reduced doses, helps preserve long-term brain function while still controlling the disease.

Will treatment affect my memory or thinking? It can, especially with whole-brain radiation, which is why modern treatment uses lower doses, memory-sparing techniques, and chemotherapy-first approaches to reduce this risk. Your team will weigh these effects against the need to control the lymphoma and will monitor your cognition during and after treatment.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.