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A woman who had a cancerous tumour in her arm is now in remission despite receiving no treatment. This is thought to be due to a biopsy she had to diagnose the growth causing an immune response against the cancer.

She is one of just nine known cases where a biopsy led to a cancer of this type, which affected her connective tissue, disappearing within a few weeks.

“It’s extremely remarkable,” says at the Centre for Immunology of Marseille-Luminy in France, who wasn’t involved in the case. “It really suggests some kind of immune activation in response to the injury of the biopsy, because it had extremely rapid effects on tumour growth.”

The woman, aged 59, noticed the rapidly growing lump a few weeks before she sought help, at which point it was 2 centimetres wide. “It had been progressing rapidly, causing some pain and discomfort; she was concerned,” says at Marshfield Clinic Health System in Wisconsin, who treated the woman.

Sharma and his colleagues marked the tumour’s location with tattoo ink and took a biopsy by briefly inserting a thin needle into it. This revealed that the lump, which was located in the connective tissue between the woman’s skin and muscle, was a tumour called myxofibrosarcoma that contained aggressive cancer cells. “It was likely to spread, [and] cancers kill by spreading,” says Sharma.

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Two weeks later, the woman returned for surgery to remove the tumour, but the clinicians were surprised to discover it had completely disappeared. “She said that after the biopsy, it had started to go down within three [to] four days,” says Sharma.

To make sure the tumour really had gone, the team surgically excised the tissue surrounding where it had been, which confirmed there were no cancer cells. “The timing of the biopsy and resolution suggests there’s an immune reaction occurring,” says Sharma. Any type of cancer disappearing after biopsy is highly unusual, but this has been most commonly reported for cancers that are more easily recognised by the immune system, such as those of the skin, he says.

Taking a biopsy may cause some cancer cells to die and release inflammatory signals that activate first-responder immune cells, such as natural killer cells, to kill off damaged tumour tissue within hours to days, says Sharma. This may then cause even more proteins that are specifically in or on cancer cells to be spewed out, says Sharma. In turn, T cells of the immune system probably also become activated to recognise and destroy cancer cells, he says.

But, of course, this doesn’t occur – at least in a meaningful way – in most people, so the lucky few probably have certain genetic factors and environmental exposures that mean their immune systems can respond in this way, says Lawrence.

Unpicking what those are, such as by analysing the genomes and medical histories of these rare cases, could reveal ways to improve general responses to cancer therapy, says Lawrence.

Analysing how the immune system of mice with cancer responds to minor tissue injuries could also help to reveal what’s going on, says at the Francis Crick Institute in London. “If we understand the mechanism by which biopsy is making those cells visible to the immune system, we could harness it and develop drugs that do that too,” he says.

Sharma says the team hopes to explore this in the next few years, after compiling a database of similar cases.