Tumour-infiltrating lymphocytes are established as prognostic in breast cancer, and high pre-treatment levels predict better response to systemic therapy. This review from the International Immuno-Oncology Biomarker Working Group asks the question nobody has answered: do they predict response to radiotherapy?
The honest answer the review gives is that clinical evidence is scarce. There are plausible mechanisms in both directions — radiotherapy can provoke immune activation, and an immunologically active tumour might respond differently — but the trials that would settle it have not been run, largely because TIL scoring has not been collected in radiotherapy trials.
The working group's ask is procedural rather than clinical: standardised TIL reporting, so that the question becomes answerable from trials already under way. That is a modest request with real consequences, because a biomarker that is not recorded cannot be analysed retrospectively however many patients pass through. For a clinician today there is nothing to change; for anyone designing or contributing to a breast radiotherapy trial, there is.
- Do not use TIL score to make radiotherapy decisions — there is no evidence base for it.
- Continue reporting TILs where your pathology service already does; the prognostic and systemic-therapy value is established.
- If your centre contributes to breast radiotherapy trials, ask whether TILs are being recorded.
- Standardised scoring is the bottleneck, not tissue availability — the blocks exist.
Why it matters
A biomarker that is not collected in a trial cannot answer a question later, however many patients the trial enrols.
Don't overread it
This is a review and a call for standardised reporting, not evidence that TILs predict radiotherapy response.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for oncology, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free