British scientists have devised a “pill on a string” to help doctors detect esophageal cancer at an early stage.

The development, reported in the journal Nature Genetics, could mark an improvement over diagnosis through biopsies, said researchers at the University of Cambridge.

The pill dissolves when swallowed to allow a tiny sponge inside to scrape off cells when withdrawn up the gullet that can be analyzed for evidence of cancer, such as genetic changes.

Tests of the pill, involving 23 patients over a three-year period, found it to be an effective way to flag esophageal cancer early, Rebecca Fitzgerald, with the Medical Research Council Cancer Research Unit at the University of Cambridge.

"If you're taking a biopsy, this relies on your hitting the right spot,” where cancerous tissue may be present, she said. “Using the [sponge] appears to remove some of this game of chance."

The researchers found that there appeared to be a tipping point, where a patient would go from having lots of individual genetic mutations, but no cancer, to the development of the disease.

"We know very little about how you go from pre-cancer to cancer — and this is particularly the case in esophageal cancer,” said co-researcher Co-author Dr Caryn Ross-Innes. “But we are now a step closer to understanding which are the important mutations that tip the condition over into a potentially deadly form of cancer."