Ex vivo drug sensitivity screening in blood cancers (EXALT)

What it measures. Leukaemia and lymphoma cells survive a few days outside the body, long enough to test a hundred or more approved drugs directly on them. Two laboratory approaches dominate: viability screening of purified cells in 384-well plates, developed at the Institute for Molecular Medicine Finland (FIMM) in Helsinki as drug sensitivity and resistance testing, and image-based single-cell screening (pharmacoscopy) at CeMM in Vienna, which reads how each drug shifts the ratio of malignant to normal cells in a mixed sample so the result reflects selective killing. The readout is a ranked list of drugs the patient's own cells respond to.

Evidence. In the Vienna EXALT trial (Cancer Discovery 2022), 56 patients with relapsed aggressive blood cancers were treated on the basis of image-based screening; 54 per cent had a progression-free survival at least 1.3 times longer than on their previous line of therapy, and a group of exceptional responders emerged. The Helsinki group runs a functional precision medicine tumour board for acute myeloid leukaemia and reported similar feasibility. Randomised trials comparing functional selection with standard choice are underway.

Who should have it and what changes. Today this is offered inside trials and at a few academic centres for patients with relapsed or refractory leukaemia, lymphoma or myeloma who have exhausted standard options. A positive screen points to a repurposed or off-label drug that the treating team may use; a negative screen argues for a trial of something new. Turnaround is under a week, faster than organoid testing for solid tumours, and the cost is that of a specialised laboratory assay. No screening platform of this kind is regulator-cleared as a diagnostic.