Over several years, he fine-tuned a mixture called Plasmax, which contains around 60 nutrients and chemicals at the concentrations usually found in human blood. “It was a side project—just a way of obtaining a better tool to do better research,” Tardito says. “But from the beginning, we noticed that the medium was making a difference.”

His colleague Johan Vande Voorde realized that cancer cells, when grown in Plasmax, behave more like they would in actual tumors, without several weird behaviors that are triggered by commercially available media. For example, DMEM contains a substance called pyruvate at 10 times its normal concentration in blood. These abnormal levels force cancer cells to grow as if they were starved of oxygen, even when the gas is abundantly present. In DMEM, the cells act as if they were being choked. In Plasmax, they do not.

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Unlike DMEM, Plasmax also contains selenium, an essential mineral. By comparing the two media, Vande Voorde showed that when breast cancer cells are grown at low densities, they die in the absence of selenium, but flourish in its presence. That’s a little worrying. Several researchers have tested selenium supplements as a way of preventing cancer, but despite many studies there’s no strong evidence for a protective effect. Instead, Tardito wonders if such supplements could be risky: If selenium allows cancer cells to survive in sparse populations, it might make it easier for fragments of tumors to spread to other parts of the body. “We’ll need to follow that up in animal studies,” he says.

David Sabatini of the Whitehead Institute for Biomedical Research has also been mixing up his own culture medium that mimics the nutrient levels of human blood. In 2017, he showed that cancer cells grown in this mixture are much less sensitive to a chemotherapy drug called Adrucil.

These results come at an interesting time. In recent years, cancer biologists have been grappling with a possible reproducibility crisis, in which results from several experiments involving lab-grown cells can’t be repeated by other teams. More broadly, researchers have struggled to translate the results of basic experiments involving such cells into new treatments that actually help cancer patients. Although there are many possible reasons for these problems, Tardito wonders whether he and his colleagues might get better results if they grow their cells in more realistic media.

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“Could these new media uncover vulnerabilities of cancer cells more robustly than before?” adds Chi Van Dang of the Wistar Institute, who also wants to know how immune cells might react under these more physiological conditions. “Could these media help us to understand immunotherapy better?”