Lynch syndrome

People with Lynch syndrome should be offered daily aspirin, which roughly halves bowel cancer risk with a delayed and durable effect. Whether a lower dose (as tested in CAPP3) is as effective, and whether the finding extends to the general population, are separate questions.

Because Lynch syndrome tumours make the same abnormal proteins in almost every patient, a single vaccine could in principle be given to carriers before cancer develops. This small trial showed the concept is safe and immunogenic; whether it prevents cancer requires the randomised trials now being planned.

It is the second half of the argument for unselected germline testing, and it widens the target beyond BRCA: two thirds of the actionable inherited findings in prostate cancer are in other genes, including the mismatch repair genes that open a checkpoint inhibitor route.

It is the argument for sequencing every man with advanced prostate cancer rather than only the ones who look high risk: the phenotype is uncommon, it is invisible clinically, it opens the only durable immunotherapy route in this disease, and in one man in five it also identifies Lynch syndrome in the family.

The germline finding is the practical lesson: a meaningful minority of biliary cancer patients carry inherited repair-gene mutations that matter for PARP inhibitor eligibility and for their relatives, which argues for germline testing alongside tumour sequencing.

Guidelines recommending universal mismatch repair testing in pancreatic cancer, by immunohistochemistry or sequencing rather than PCR alone, rest on this and similar series.

It gives a cheap way to find the rare men who could benefit from checkpoint blockade: an immunohistochemical stain on the highest-grade primary tumours, where the yield is twenty times higher than average. It also shows the loss is clonal and early, so the diagnostic block is an adequate place to look.

The evidence that made germline testing standard for every man with metastatic prostate cancer, whatever his family history. It changes his treatment, because PARP inhibitors and platinum work better in these tumours, and it changes his relatives' screening, because BRCA2 carries breast, ovarian and pancreatic risk as well.