The protocol was built around American medicine. The patients were European.

An oral contraceptive trial had stalled across Europe and nobody could say why. It was sitting in the schedule of assessments: four Pap smears. In the US, where that screening frequency is routine standard of care, it read as unremarkable, so it went through design without a flag. European women aren't screened anywhere near that often. Being asked for four was enough to stop them enrolling.

It stayed undiagnosed because catching it meant holding two countries' standard of care in your head at once, and very few people work across healthcare systems closely enough to feel the gap. We caught it because we had. It shouldn't take an outsider to find something written into the schedule of assessments.