Potency only counts where the drug arrives.
A compound has an activity. A tumour has a geometry. The number that decides an outcome is the overlap between them, and it is the number a well plate cannot produce.
The blind spot
A potency value is a statement about a concentration: at this concentration, this fraction of cells responds. It says nothing about whether that concentration ever exists anywhere in a tumour.
So two compounds can carry the same potency and behave nothing alike in tissue, and the ranking that came off the plate can be exactly inverted by the geometry. This is not an edge case. It is one of the ordinary ways a programme spends two years finding out something it could have asked at the start.
What you get back
Exposure is the overlap made explicit: how much of the mass the compound actually covers, for how long, and where it does not.
- The share of tumour volume that reaches a therapeutic concentration, and how long it holds
- Where the shortfall is, named as a region rather than buried in an average
- How that moves with dose, with schedule, and between candidates
- Which candidate covers most of the tumour it is meant to treat — not which is most potent
The decision it changes
Where a region is never reached, LURA says so and names it, instead of returning a lower average that hides it. A named failure is a design brief. An averaged one is a surprise in year three.
That changes what a portfolio review is for. Not defending a ranking, but knowing which candidate covers the tumour it is meant to treat — and what it would take to cover the rest.