Pick a patient with advanced pancreatic cancer, a few months of life left on the standard treatments, in an oncologist's office this week. The oncologist can now offer a drug that goes after the thing driving the tumour.

That thing is RAS, a protein that works like a light switch inside the cell. Switched on, it tells the cell to divide. Healthy cells flip it off again. In most pancreatic cancers a mutation jams the switch in the on position, so the growth signal never stops.

For decades RAS looked untouchable. The protein is small and smooth, with no obvious pocket for a drug to grip, and it holds its natural fuel molecule very tightly, so a rival molecule has a hard time pushing in. Researchers called it undruggable, and the label stuck for a generation.

The FDA has now approved daraxonrasib for pancreatic cancer. The trial behind the approval showed survival nearly doubled, according to the oncologist's explainer published by The Good Men Project.

"Nearly doubled" is a ratio of survival times. What it means in months depends on the starting point, and in advanced pancreatic cancer the starting point is short. Doubling a short time is a real gain for the person living it, and it is still a gain measured in a modest number of months. The trial showed the drug can substantially extend survival for some patients, which also means some patients get less.

The stage is a shipping product. The drug has cleared the regulator, which is the gate between a trial result and a prescription pad.

The patient in that office is weighing a drug whose benefit is known as an average across a trial population. Nobody can say which side of the average they will land on. They will start treatment with the early numbers in hand and the long tail of the survival curve still unwritten.

That tail is the next gate. Longer follow-up of the people already treated will show whether some of them live well beyond the average, or whether the curve simply shifts later and then falls the same way. By the time the patient starting this week reaches their first scans, their oncologist will have only the early curve. Each additional year of follow-up will tell the next patient what this one could not be told.