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Two brain tumours can look identical under the microscope yet be entirely different diseases. Since 2021, molecular markers like IDH and MGMT are part of the diagnosis itself — and they shape your treatment.
If you or someone you love has just been diagnosed with a brain tumour, you may have heard the words "IDH", "MGMT" or "WHO grade" and felt completely lost. You deserve a plain explanation. This page is that explanation — written and reviewed by our neuro-oncology team for patients and families facing a brain tumour diagnosis.
For decades, a brain tumour was named almost entirely by how its cells looked under a microscope. That changed in 2021. The World Health Organization rewrote the rulebook so that the genes inside the tumour are now part of the diagnosis itself. The practical result: a molecular test done on your biopsy can change the name of your tumour, its grade, your expected outlook, and which treatments are recommended. Skipping it can leave the picture incomplete.
The WHO 2021 Classification of Tumours of the Central Nervous System (5th edition) was the first to make molecular markers — such as IDH mutation and 1p/19q co-deletion — a required part of the integrated diagnosis for many gliomas, not just an optional extra. A tumour can even be classified as Grade 4 on molecular features alone. (Source: WHO Classification of CNS Tumours, 5th ed., 2021; endorsed in NCCN and EANO glioma guidelines.)
This is the single most important idea behind molecular testing. The old microscope-only approach grouped tumours by appearance. Genetics revealed that those look-alike groups actually contained very different diseases — with very different outlooks and treatments.
A pathologist examined the tumour cells under a microscope and named the tumour by their shape, size, and how disordered they looked. This is called histology. It is still essential — but on its own it could place two biologically different tumours into the same box, leading to one-size-fits-all treatment.
Today, the microscope findings are combined with molecular markers from the same tissue. The result is an "integrated diagnosis" — the official WHO 2021 approach. It separates look-alike tumours into their true types, so treatment can be matched to the actual biology rather than appearance alone.
The molecular result can shift your diagnosis, grade and outlook, and change the recommended chemotherapy and radiation plan. Because of this, both NCCN and EANO recommend molecular testing before a glioma treatment plan is finalised. If yours was skipped, ask about it.
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We walk this journey with you. Talk to CION's neuro-oncology team about IDH, MGMT and 1p/19q testing — and what your results mean for your plan.
Your pathologist and oncologist choose a panel that fits your tumour type — not every tumour needs every test. These are the markers that most often change a glioma diagnosis and plan under the WHO 2021 classification. Tap each one to learn what it means.
Marker selection follows WHO 2021, NCCN and EANO guidance. The exact panel is chosen by your pathologist and neuro-oncologist for your specific tumour.
Molecular testing does not usually mean an extra operation. Here is the path most patients follow at CION:
While you wait for results, your essential care — such as steroid and seizure management and recovery after surgery — continues without delay. The molecular results then refine the longer-term chemotherapy and radiation plan.
You usually do not need a fresh biopsy for molecular testing if you have already had surgery. Most labs can run IDH, MGMT and 1p/19q on the stored paraffin-embedded tissue block from your original procedure — even months later. CION helps you trace and transfer that tissue, so a second opinion need not mean a second operation. (Aligned with NCCN and EANO recommendations to confirm molecular markers before finalising glioma treatment.)
For a glioma, molecular testing is not a luxury — current NCCN and EANO guidelines treat it as part of the standard diagnostic workup. A free second opinion is especially worthwhile if any of the following apply to you:
If you would like our neuro-oncology team to review your reports, start at the brain cancer and tumour hub or call 18002028726 for a free, confidential second opinion. Decisions here are made for healing, not billing.
Share your biopsy or surgery report with CION's neuro-oncology tumour board. We'll confirm which molecular markers were tested, what's missing, and what it means for your plan.
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Start Your Story. Book Free Consultation.Molecular testing looks at the genes and DNA changes inside your tumour tissue — not just how the cells look under a microscope. A small piece of tumour (from surgery or a stereotactic biopsy) is sent to a specialised lab. The lab checks for specific markers such as IDH mutation, MGMT promoter methylation, and 1p/19q co-deletion. Since the WHO 2021 classification, these markers are part of the official diagnosis itself. Two tumours that look identical under the microscope can be completely different diseases at the molecular level — and need different treatment. At CION, molecular testing is arranged as standard on every malignant glioma sample.
Before 2021, brain tumours were named and graded mostly by how the cells looked (histology). The WHO 2021 Classification of Tumours of the Central Nervous System made molecular markers part of the diagnosis, not an optional add-on. For example, an "astrocytoma" is now defined partly by its IDH status, and a tumour can be graded Grade 4 on molecular features even without the classic microscope findings. This is why a diagnosis made without molecular testing may be incomplete under current guidelines. The shift means more accurate naming, more accurate grading, and treatment matched to the true biology of the tumour.
The core markers for gliomas under WHO 2021 are: IDH1/IDH2 mutation (the single most important prognostic marker — IDH-mutant tumours behave more favourably); 1p/19q co-deletion (defines oligodendroglioma when combined with IDH mutation); and MGMT promoter methylation (predicts how well alkylating chemotherapy is likely to work in glioblastoma). Other markers your neuro-oncology team may check include ATRX, TERT promoter, EGFR amplification, +7/−10, and CDKN2A/B deletion. Not every tumour needs every test — your pathologist and oncologist choose the panel that fits your tumour type.
In most cases, no. Molecular tests are run on the same tissue already taken during your surgery or biopsy — there is no second operation just for testing. If you have already had surgery elsewhere, the stored paraffin block or slides from that procedure can usually be retrieved and sent for molecular analysis. If no tissue was ever sampled, a minimally invasive stereotactic biopsy (coordinated with our accredited neurosurgical partners) may be needed first. CION helps you trace and transfer existing tissue so testing can proceed without delay.
It depends on the test. Immunohistochemistry for IDH and ATRX is often available within a few days. MGMT methylation and 1p/19q testing typically take about 1 to 2 weeks. Full next-generation sequencing (NGS) panels can take 2 to 3 weeks. Your treatment is planned so that essential steps (like steroid and seizure management, or wound healing after surgery) continue while results are awaited — molecular results then refine the longer-term chemotherapy and radiation plan. We keep you informed at each stage so the wait never feels like a black box.
Very often, yes. Molecular results can change the diagnosis name, the grade, the expected prognosis, and the choice of chemotherapy and radiation. For example, MGMT methylation status helps predict the likely benefit of alkylating chemotherapy in glioblastoma; IDH status separates tumours with very different outlooks; and 1p/19q co-deletion identifies oligodendrogliomas that tend to respond well to combined chemo-radiation. Because of this, NCCN and EANO guidelines recommend molecular testing before finalising the treatment plan for gliomas. This is a strong reason to seek a second opinion if testing was skipped.
CION delivers the parts of brain tumour care it is equipped for directly — medical and systemic therapy, radiation therapy (IMRT/IGRT), imaging and diagnosis coordination, steroid and seizure management, and supportive care. Molecular testing is arranged through accredited specialist laboratories, and any tissue sampling (such as a stereotactic biopsy) is coordinated with our accredited neurosurgical partners. Our neuro-oncology tumour board interprets every result for you and translates it into a clear, personalised plan — so you understand exactly what each marker means for your treatment and outlook.
Browse our complete guide to brain tumours and brain cancer — symptoms, scans, tumour types, treatment, prognosis and life after treatment. Tap any topic to read more.