Tumour mutational burden (TMB)

For the first time a randomised trial suggests that a vaccine tailored to an individual's tumour can reduce relapse when combined with immunotherapy, which is a proof of concept for a field that had failed for decades. Nothing changes for patients yet: the trial was small, the confidence interval crossed one, and the phase 3 trial in melanoma (and parallel trials in lung and other cancers) must confirm it. If it does, personalised mRNA vaccines could become a routine adjunct to checkpoint inhibitors after surgery.

Pancreatic cancer was thought to be immunologically inert because of its low mutation burden; this study showed that with the right vaccine platform its few neoantigens can still be targeted. It is the strongest human evidence so far that personalised cancer vaccines can generate durable, tumour-specific immunity, and it justifies the randomised trials now running in pancreatic cancer and melanoma. Benefit is not yet proven, because responders may simply have had more immunogenic tumours.

Every colorectal cancer should be tested for mismatch repair deficiency, because patients whose metastatic tumour is dMMR should receive pembrolizumab rather than chemotherapy as first treatment, gaining a much better chance of durable remission with fewer side effects. About a third of dMMR tumours do not respond initially, so early scans are essential and chemotherapy remains available. The trial does not apply to the 95% of colorectal cancers that are mismatch-repair proficient.

Cancers are defined as much by the tissue they come from as by the mutations they carry, which is why the same drug can work in one organ and fail in another with the same mutation. TCGA is the shared public dataset behind most modern biomarkers and target discovery.

This paper established a new regulatory paradigm: a drug approved for a molecular feature regardless of organ. It made MSI/MMR testing standard across advanced cancers and remains the clearest example of a biomarker that works across histologies. It also anchored the idea that mutation load, via neoantigens, is what makes tumours visible to T cells.

This small trial explained why colorectal cancer had seemed immune-resistant (most is MMR-proficient) and established the principle that a genomic feature, not the tissue of origin, can predict immunotherapy response. It led directly to the 2017 tissue-agnostic approval of pembrolizumab and to routine MMR/MSI testing of many cancers. Every patient with advanced dMMR cancer should now be considered for checkpoint blockade.

There are not thousands of cancer genes, and any one patient's tumour is driven by only a few of them. That makes targeted sequencing panels sensible, but because most drivers are lost tumour suppressors, drugs exist for only a minority, which is why the same group turned to early detection.