biomarker

Loss of one copy each of chromosome arms 1p and 19q, together with an IDH mutation, defines oligodendroglioma in the WHO 2021 classification. It predicts a slower course and a good response to chemotherapy, and separates oligodendroglioma from astrocytoma.

An extra stretch of chromosome 9 that carries both of the molecules a tumour uses to switch off T cells, plus the enzyme that turns them up further. Nearly every classical Hodgkin lymphoma has it, which is why checkpoint drugs work so well there and so poorly in most other lymphomas.

AKT1 E17K is a single hotspot mutation, in about 3 to 5 percent of hormone-receptor-positive breast cancers, that switches on the AKT kinase directly. It is one of the three alterations that qualify a patient for capivasertib.

An ALK fusion, usually EML4::ALK, is a swapped piece of chromosome 2 that turns the ALK kinase on permanently in about 4 percent of lung adenocarcinomas. Seven ALK inhibitors are approved for it, including alectinib after surgery.

After a lung cancer stops responding to an ALK-blocking tablet, finding a change inside the ALK protein itself is good news: it means the cancer still depends on ALK, and a later-generation tablet is likely to work. Finding none means the opposite.

Extra copies of the gene for the androgen receptor. It is almost never present before hormone treatment and is found in about half of prostate cancers that have become resistant to it, which is why the stage the sample was taken at matters more than the result itself.

A change in the part of the androgen receptor that hormone drugs attach to. Depending on which change it is, another hormone the man is already taking can switch the receptor on, or the blocking drug can start behaving as an activating one.

AR-V7 is a shortened androgen receptor that lacks the part hormone drugs bind, so it stays active without testosterone. Found in circulating tumour cells, it predicts poor response to abiraterone and enzalutamide, but no label uses it yet.

B7-H3 is an immune checkpoint protein overexpressed on small-cell lung, prostate and many solid tumours. Ifinatamab deruxtecan is in phase 3 for small-cell lung cancer without an expression cut-off; nothing is approved.

A change in the pocket of the survival protein BCL-2 where venetoclax has to fit. The protein still works and the drug no longer binds it. It can be detected in blood months before the disease starts growing again.

A swap of DNA that puts the survival gene BCL2 next to an antibody gene, so the cell makes far too much of a protein that stops it dying. It is the founding event of most follicular lymphomas and it happens in the bone marrow, often years before anything is wrong.

BCMA is the plasma-cell antigen behind the myeloma bispecifics and CAR-T cells. None of their labels requires a BCMA test; expression is near-universal, and loss through BCMA gene deletion is a documented escape route.

T315I is the gatekeeper mutation in the ABL1 kinase that defeats imatinib, dasatinib, nilotinib and bosutinib. Ponatinib and asciminib are the two drugs approved for it.

The BCR::ABL1 fusion is the Philadelphia chromosome that defines chronic myeloid leukaemia and some acute lymphoblastic leukaemia. Its transcript level in blood, on the international scale, is how response to tyrosine kinase inhibitors is measured and when treatment can be stopped.

Class II and III BRAF mutations sit outside codon 600 and signal as pairs (class II) or by leaning on RAS (class III). Approved BRAF inhibitors do not work on them, and no drug is yet approved for them; pan-RAF inhibitors are in trials.

A BRAF fusion joins another gene to the BRAF kinase, most often KIAA1549 in paediatric low-grade glioma. Tovorafenib is approved for children whose relapsed low-grade glioma carries a BRAF fusion or V600 mutation.

V600E is the BRAF change that drives half of melanomas and many thyroid, bowel, lung and brain tumours. BRAF plus MEK inhibitors are approved for it in melanoma, lung, thyroid and, tumour-agnostically, any solid tumour; in bowel cancer it is treated with encorafenib and cetuximab.

DNA repair genes. Inheriting a broken copy raises breast and ovarian cancer risk, but tumours that lose them become uniquely vulnerable to PARP inhibitors and platinum.

A change in the enzyme BTK at the exact point where the drug grips it. The enzyme keeps working and the drug no longer holds, which is the usual reason a BTK inhibitor stops working after it has been working well.

c-Met overexpression is a stain, not a gene change: strong (3+) membrane staining in at least half of tumour cells. It selects telisotuzumab vedotin, an antibody-drug conjugate, in previously treated non-squamous lung cancer.

CD19 is the B-cell surface protein that blinatumomab, CAR-T cells and several antibodies aim at. Blinatumomab's label requires CD19-positive leukaemia; the CAR-T labels assume it, and losing CD19 is the commonest way the disease escapes.

CD20 is the B-cell antigen rituximab made famous. Rituximab and obinutuzumab labels are written for CD20-positive lymphoma and leukaemia; the newer CD20 x CD3 bispecifics assume it.

CD22 is a second B-cell antigen, kept even when CD19 is lost. Inotuzumab ozogamicin is labelled for CD22-positive acute lymphoblastic leukaemia.

CD30 is the antigen of Hodgkin Reed-Sternberg cells and anaplastic large cell lymphoma. Brentuximab vedotin is labelled for Hodgkin lymphoma without a CD30 test and for peripheral T-cell lymphomas that express it.

CD33 is a myeloid antigen on the blasts of about 90 percent of acute myeloid leukaemias. Gemtuzumab ozogamicin's label requires CD33-positive disease.

CD38 is on almost every myeloma cell, so daratumumab and isatuximab are given without testing for it. The stain matters afterwards: CD38 falls after treatment and can confuse flow cytometry and blood typing.

A change in the signalling tail of part of the B-cell receptor that leaves the receptor switched on without needing anything to bind it. It marks a group of large B-cell lymphomas that depend on that signal, and therefore on the enzyme BTK.

The classic 'CEA' tumour marker measured in blood, also present on the cell surface where ADCs can reach it.

CEACAM5 is the cell-surface form of the tumour marker CEA, high on many lung and bowel cancers. Tusamitamab ravtansine was tested in CEACAM5-high lung cancer but failed its phase 3 and no approval exists.

How much of the DNA floating in a blood sample came from the cancer. Above a few per cent, a plasma test finds what a biopsy would find; below it, a negative result means the test could not see, not that there is nothing there.

Claudin 18.2 is a tight-junction protein exposed on stomach cancer cells. Zolbetuximab requires at least 75 percent of tumour cells to stain moderately or strongly, the strictest expression threshold in any current label.

A ctDNA MRD test looks for the tumour's own mutations in blood after surgery. Detection predicts relapse months before scans, and in 2026 the FDA approved Signatera as the companion test selecting bladder cancer patients for adjuvant atezolizumab.

DLL3 sits on the surface of about 85 percent of small-cell lung cancers and almost no normal adult tissue. Tarlatamab is given without a DLL3 test.

dMMR means one of the four mismatch repair proteins is missing from the tumour cell nuclei on a stain. It is the tissue-level twin of MSI-high and opens checkpoint immunotherapy in endometrial, bowel and many other cancers.

A stain showing that a lymphoma makes a lot of both the growth protein MYC and the survival protein BCL2, without the genes being rearranged. It predicts a worse course, but on its own it does not change the treatment.

A lymphoma that carries a rearrangement of MYC, the gene that drives growth, together with one of BCL2 or BCL6, the genes that stop a cell dying. Having both is far worse than having either, and it usually means a stronger treatment than standard R-CHOP.

A change in the EGFR protein that removes the anchor point the newest lung cancer pills grip. Whether it can be worked around depends on whether it sits on the same copy of the gene as the earlier resistance change or on the other copy.

An exon 19 deletion removes a few amino acids from the EGFR kinase and leaves it switched on. With L858R it makes up about 85 percent of EGFR-mutant lung cancer and is the classic gate for osimertinib and the other EGFR inhibitors.

Exon 20 insertions add amino acids after the C-helix of EGFR and make the kinase resistant to the usual EGFR tablets. They account for about a tenth of EGFR mutations and have their own drugs: amivantamab with chemotherapy and sunvozertinib.

L858R is a single letter change in exon 21 of EGFR that keeps the kinase active. It is the second commonest sensitising mutation and shares every EGFR inhibitor label with the exon 19 deletion.

T790M is the gatekeeper mutation that lung cancers acquire to escape first- and second-generation EGFR inhibitors. Finding it, in tissue or blood, is the historic gate for osimertinib after an earlier EGFR drug.

An epigenetic clock reads chemical marks on DNA and estimates how old the body looks, which is not always the age on a birth certificate. In survivors of childhood cancer the clock runs ahead of chronological age, and the gap is larger after radiotherapy and after certain chemotherapy drugs. What the gap means for any one person is not yet known, and the clocks do not agree with each other.

ER status is whether the tumour's cells carry the oestrogen receptor, read by staining nuclei. One percent or more of stained nuclei is positive and means hormone-blocking treatment can work; 1 to 10 percent is 'low positive' and behaves more like negative.

ESR1 mutations arise in the oestrogen receptor's ligand-binding domain after aromatase inhibitor treatment, letting the receptor work without oestrogen. They are usually found in a blood test and select the oral SERDs elacestrant and imlunestrant.

A change in an enzyme that puts a chemical silencing mark on DNA. The altered enzyme adds too much of the mark, which keeps a lymphoma cell locked in the state it should have grown out of. It is the one lymphoma mutation that currently selects a tablet.

FcRH5 is a third myeloma surface target after BCMA and GPRC5D. Cevostamab, the FcRH5 x CD3 bispecific, is in phase 3; no approval or threshold exists yet.

FGFR2 fusions occur in 10 to 15 percent of intrahepatic bile duct cancers and almost nowhere else. Pemigatinib and futibatinib are approved for them after a first chemotherapy.

FGFR3 point mutations and TACC3 fusions drive about 15 to 20 percent of advanced bladder cancers. Erdafitinib is approved for tumours with these 'susceptible' alterations after one prior treatment.

FLT3-ITD is a duplicated stretch of the FLT3 receptor gene found in about a quarter of acute myeloid leukaemias; it makes relapse more likely and is treated with midostaurin, quizartinib or gilteritinib.

FLT3-TKD mutations are point changes in the kinase's activation loop, found in about 7 percent of acute myeloid leukaemias. Midostaurin and gilteritinib labels cover them; quizartinib's does not.

Folate receptor alpha is a surface protein on most high-grade serous ovarian cancers. Mirvetuximab soravtansine requires FRα-positive disease, scored as at least 75 percent of cells with moderate or strong staining on the Ventana FOLR1 assay.

Chemotherapy and radiotherapy select for blood stem cells carrying particular mutations, and in a small minority one of those clones becomes a leukaemia. The useful question is not whether a clone is there but whether it will progress: most never do, and nothing has been shown to stop one that does.

A germline BRCA1 or BRCA2 variant is inherited and present in every cell, found by a blood test. It selects PARP inhibitors in breast, ovarian, pancreatic and prostate cancer and tells relatives they may carry it too.

GPRC5D is a receptor on myeloma cells and in hair follicles, nails and taste buds. Talquetamab targets it without any test, and the side effects on skin, nails and taste follow from where it is expressed.

H3 K27M is a single change in a histone that defines diffuse midline glioma, including the brain-stem tumour DIPG. In 2025 dordaviprone became the first drug approved for tumours carrying it.

A HER2 mutation is a change in the gene's kinase domain, most often an exon 20 insertion, found in about 2 to 3 percent of lung adenocarcinomas. It is a different thing from HER2 amplification or overexpression, and it selects trastuzumab deruxtecan and, since 2025, zongertinib in lung cancer.

IHC 0 is no HER2 staining, or faint staining in 10 percent or fewer cells. It is HER2-negative, but the label now separates true zero from 'IHC 0 with membrane staining', the ultralow group that trastuzumab deruxtecan can treat in hormone-receptor-positive breast cancer.

IHC 1+ is faint, incomplete HER2 staining. It was called HER2-negative for twenty years; since 2022 it is the larger half of HER2-low, which trastuzumab deruxtecan treats in breast cancer.

IHC 2+ is the in-between HER2 result: moderate staining that cannot be called positive or negative by eye, so the laboratory runs an ISH gene test. 2+ with amplification is HER2-positive; 2+ without it is HER2-low.

IHC 3+ means strong, complete membrane staining for HER2 in more than 10 percent of tumour cells. It is HER2-positive without needing a gene test and is the gate for trastuzumab, its combinations and antibody-drug conjugates in breast, stomach, biliary and, since 2024, any solid tumour.