It was a case that baffled everyone involved. The 74-year-old woman had initially been troubled by a rash that wouldn’t go away. By the time she arrived at the hospital, her lower right leg was covered in waxy lumps, eruptions of angry red and livid purple. Tests confirmed the worst suspicions: it was carcinoma, a form of skin cancer.

The future looked bleak. Given the spread of the tumours, radiotherapy would not have been effective; nor could the doctors dig the tumours from the skin. Amputation was perhaps the best option, says Alan Irvine, the patient’s doctor at St James’ Hospital, Dublin – but at her age, she was unlikely to adapt well to a prosthetic limb. After a long and frank discussion, they decided to wait as they weighed up the options. “We had a lot of agonising for what to do,” says Irvine.

Then the “miracle” started. Despite receiving no treatment at all, the tumours were shrinking and shrivelling before their eyes. “We watched for a period of a few months and the tumours just disappeared,” says Irvine. After 20 weeks, the patient was cancer-free. “There had been no doubt about her diagnosis,” he says. “But now there was nothing in the biopsies, or the scans.”

Somehow, she had healed herself of arguably our most feared disease. “Everyone was thrilled, and a bit puzzled,” Irvine says, with some understatement. “It shows that it is possible for the body to clear cancer – even if it is incredibly rare.”

The question is, how? Irvine’s patient believed it was the hand of God; she had kissed a religious relic just before the healing set in. But scientists are instead looking to the underlying biology of so-called “spontaneous regression” to hunt for clues that could make these rare cases of self-healing more common. “If you can train the body to do this on a broader scale, you could have something that’s very widely applicable,” says Irvine.