Study finds antibiotics may worsen melanoma: Here's how

The use of broad-spectrum antibiotics in mice with malignant melanoma, an aggressive form of skin cancer, accelerated their metastatic bone growth, likely because the drugs depleted the mice's intestinal flora and weakened their immune response, according to a new study by researchers at Emory University in Atlanta.

The researchers hypothesized that using antibiotics to deplete the gut microbiome of mice would affect their intestinal immune cells and thus alter their immune response, leading to accelerated bone metastasis. They injected B16‐F10 melanoma cells into the hearts and bones of mice that had been treated with broad‐spectrum antibiotics. As predicted, the antibiotic injections accelerated bone metastatic growth in those mice, compared with control mice that had not received the shots.

The study revealed the mechanism for the metastatic growth of melanoma. Flow cytometric analysis of Peyer's patches and bone-marrow cells within tumor lesions revealed that microbiome depletion prevented the melanoma‐induced expansion of intestinal NK and Th1 cells and their migration from the gut to tumor‐bearing bones. Direct measurement of NK and Th1 cells migration using Kaede mice, a strain expressing a photo‐convertible fluorescent protein that allows direct tracking of intestinal lymphocytes, revealed that antibiotics decreased by about eightfold the migration of NK and Th1 cells from the gut to the tumor site.

This study strongly indicates that microbiome modifications induced by antibiotics might have negative clinical consequences not only with melanoma but with other diseases as well, the researchers said.

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