Reading the cancer, or the risk of one.

The tumour already in the archive

When a biopsy or an operation has already been done, the tissue is preserved in a paraffin block and kept by the pathology department. That block is the sample. In most cases nothing new has to be taken from you, which is the part patients are most relieved to hear.

We read DNA and RNA from it. DNA finds the mutations, insertions, deletions and copy number changes. RNA is sequenced alongside because gene fusions and exon-skipping events, some of which have a drug aimed directly at them, are far more reliably caught at the RNA level than inferred from DNA. The report also covers the genomic signatures that guide immunotherapy decisions, microsatellite instability and tumour mutational burden.

The tumour, read from a tube of blood

Tumours shed fragments of their DNA into the bloodstream. A liquid biopsy separates those fragments from the patient's own circulating DNA and sequences them. It is not tied to one organ: whatever is shedding, anywhere, is what the test sees.

It earns its place in three situations. When there is no usable tissue, or not enough of it. When a repeat biopsy would be difficult or risky, which is often the case for lung, liver and pancreatic disease. And when a cancer that was responding stops responding, because a blood draw can be repeated as often as needed and will show the resistance mutation that tissue taken a year ago cannot.

What it is, and what it is not

A positive result does not mean the cancer has returned in the sense of needing treatment tomorrow. It means disease is still detectable, and that is a reason to look harder and to discuss what to do, sooner than the follow-up schedule would otherwise have allowed. A negative result is reassuring but is not a guarantee, and it does not replace the imaging and clinic visits your oncologist has planned. MRD sits alongside standard follow-up and makes it better informed.

What runs in the family, named

A minority of cancers come from a change inherited from a parent. When that change is there, the lifetime risk is substantially higher than average and it is usually higher from a younger age, which is exactly the information that makes screening worth starting early. The panel reads the genes where that is established and actionable, among them BRCA1 and BRCA2, and the Lynch syndrome genes MLH1, MSH2, MSH6, PMS2 and EPCAM.

A positive result is not a diagnosis and not a certainty. It changes three things: how early and how often you are screened, which risk-reducing options are worth discussing, and, for some cancers, which treatments would be available if one ever developed. It also puts a precise question to your relatives, who can be tested for that one change rather than the whole panel.

Looking for several cancers at once, from blood

Most cancers have no screening programme at all, and the ones that do are each aimed at a single organ. Multi-cancer early detection takes a different approach: rather than mutations, it reads the methylation pattern of DNA circulating in blood, the chemical marking that differs between healthy tissue and tumour, and asks whether any of it looks like cancer.

Over C is a multi-cancer detection blood test developed by Burning Rock. It carries a CE mark and has been granted Breakthrough Device Designation by the US FDA, which is a route to faster review rather than an approval. In its published case-control study it detected around 69 per cent of the cancers present at a specificity close to 99 per cent, in adults between 50 and 75 at average risk, for a defined set of cancers including oesophageal, liver, lung, ovarian and pancreatic.