Primary CNS LymphomaClinical Notes for Practicing Oncologists
From HDMTX-based induction (R-MPV, MATRix) and RANO-PCNSL response assessment through ASCT vs WBRT consolidation, salvage strategies including TEDDI-R and ibrutinib, and primary vitreoretinal lymphoma.
MATRix CR Rate
~49%
IELSG32 induction
ASCT 2-yr OS
~85%
IELSG32 consolidation
Ibrutinib ORR (R/R)
50-70%
Single-agent
Concurrent Ocular
15-25%
At diagnosis
How is Primary CNS Lymphoma diagnosed, worked up, and staged before committing to HDMTX-based therapy?
Primary CNS Lymphoma (PCNSL) is an extranodal non-Hodgkin lymphoma confined at diagnosis to the brain, leptomeninges, spinal cord, or eyes, without evidence of systemic disease. Over 90% are diffuse large B-cell lymphoma (DLBCL), non-germinal centre B-cell (non-GCB) subtype by Hans algorithm.
Incidence
~5%
of primary CNS tumours
Median Age
65 yrs
Rising incidence in elderly
DLBCL, non-GCB
>90%
MYD88 L265P / CD79B mutated
Immunocompromised
~2-4%
HIV, transplant — often EBV+
| Feature | Detail |
|---|---|
| Cell of origin | Post-germinal centre B-cell, non-GCB (Hans algorithm), CD20+, BCL6 variable, MUM1/IRF4 positive |
| Recurrent mutations | MYD88 L265P (~50-85%), CD79B (~60-80%) — activates NF-κB and BTK signalling, rationale for ibrutinib |
| Immune privilege | CNS lacks classic lymphatics; PD-L1 upregulation and immune evasion contribute to aggressive biology despite low proliferative fraction on imaging |
| EBV association | Nearly universal in HIV-related PCNSL and post-transplant lymphoproliferative disease; rare in immunocompetent PCNSL |
Because PCNSL is defined by the absence of systemic disease, a complete staging workup is mandatory before labelling a lesion "primary" — occult systemic or testicular lymphoma must be excluded.
| Investigation | Purpose | Key Point |
|---|---|---|
| Contrast-enhanced brain MRI | Lesion characterisation | Typically periventricular, homogeneously enhancing, restricted diffusion; multifocal in ~30-40% |
| Stereotactic biopsy | Histologic diagnosis | Preferred over resection — surgery does not improve survival and delays systemic therapy; biopsy the enhancing rim, not necrotic core |
| CSF analysis (cytology + flow cytometry) | Occult leptomeningeal disease | Positive in ~15-20%; lumbar puncture only if safe (no significant mass effect) |
| Slit-lamp ophthalmologic exam | Occult vitreoretinal lymphoma | Concurrent ocular involvement in 15-25% at diagnosis — mandatory even if asymptomatic |
| Testicular ultrasound (males >60) | Occult testicular DLBCL | Testis is a classic occult primary site that can seed CNS relapse |
| Whole-body CT or PET-CT | Exclude systemic lymphoma | Required to confirm truly "primary" CNS disease |
| Bone marrow biopsy | Exclude marrow involvement | Low yield but standard staging requirement |
| HIV testing | Immunocompromised PCNSL | Changes biology (EBV-driven) and treatment tolerance |
Avoid empirical steroids before biopsy
Even a short steroid course can dissolve the tumour on imaging, delay diagnosis by weeks, and force a repeat biopsy once the lesion re-accumulates. Reserve steroids for genuine neurological emergencies and coordinate urgent biopsy first wherever feasible.Viva Questions & Clinical Pearls
Q: Why is stereotactic biopsy preferred over resection in PCNSL?
A: Randomised and retrospective data show no survival benefit from resection, which also risks neurological deficit and delays systemic chemotherapy start; biopsy alone provides adequate tissue for diagnosis.
Q: Name three sites that must be assessed to confirm a lesion is truly "primary" CNS lymphoma.
A: Eyes (slit-lamp exam), CSF (cytology/flow), and systemic sites via whole-body CT/PET and bone marrow biopsy; testes in older males.
Q: What happens to the MRI appearance of PCNSL after steroids?
A: Rapid, often dramatic regression or complete disappearance of the enhancing lesion ("ghost tumour"), which can render subsequent biopsy non-diagnostic.
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Clinical reference only. These notes are intended to support, not replace, clinical judgment. Treatment decisions should be individualised based on patient-specific factors, local protocols, and multidisciplinary team input. Always apply clinical judgment and consult local institutional guidelines where applicable.