The problem is not that Halassy used self-experimentation as such, but that publishing her results could encourage others to reject conventional treatment and try something similar, says Sherkow. People with cancer can be particularly susceptible to trying unproven treatments.

I think they're going to try unproven treatments regardless, especially if there's a high barrier towards conventional treatment. The difference is whether they'll be swindled by quack cures or use something with demonstrable effects.

The approach seemed to be effective: over the course of the treatment, and with no serious side effects, the tumour shrank substantially and became softer. It also detached from the pectoral muscle and skin that it had been invading, making it easy to remove surgically.

Analysis of the tumour after removal showed that it was thoroughly infiltrated with immune cells called lymphocytes, suggesting that the OVT had worked as expected and provoked Halassy’s immune system to attack both the viruses and the tumour cells. “An immune response was, for sure, elicited,” says Halassy.

This seems pretty important. The regions where the cancerous and healthy tissue are mixed is are one of the limitations of surgery.

Stephen Russell, an OVT specialist who runs virotherapy biotech company Vyriad in Rochester, Minnesota, agrees that Halassy’s case suggests the viral injections worked to shrink her tumour and cause its invasive edges to recede.

But he doesn’t think her experience really breaks any new ground, because researchers are already trying to use OVT to help treat earlier-stage cancer. He isn’t aware of anyone trying two viruses sequentially, but says it isn’t possible to deduce whether this mattered in an ‘n of 1’ study.

Well, I hope we will see similar studies with larger n, to verify whether this was a fluke or not.