Add a cheap-drug factorial arm to every cooperative-group adjuvant cancer trial

Factorial designs randomise the same patients to two independent questions, sharing recruitment, follow-up and infrastructure. Add-Aspirin ran as a standalone trial; embedding similar questions as second factors in cooperative-group adjuvant trials (breast, colorectal, lung, prostate) would multiply the number of repurposing questions answered at a small marginal cost. The proposal is a policy by public trial funders (NCI cooperative groups, CRUK, EORTC) that every new large adjuvant trial include, where feasible, a factorial randomisation to a prioritised off-patent candidate, with a central committee selecting candidates and monitoring interactions.