Carl Zimmer in The New York Times:
Over the past few years, a flurry of studies have found that tumors harbor a remarkably rich array of bacteria, fungi and viruses. These surprising findings have led many scientists to rethink the nature of cancer. The medical possibilities were exciting: If tumors shed their distinctive microbes into the bloodstream, could they serve as an early marker of the disease? Or could antibiotics even shrink tumors? In 2019, a start-up dug into these findings to develop microbe-based tests for cancer. This year, regulators agreed to prioritize an upcoming trial of the company’s test because of its promise for saving lives. But now several research teams have cast doubt on three of the most prominent studies in the field, reporting that they were unable to reproduce the results. The purported tumor microbes, the critics said, were most likely mirages or the result of contamination.
“They just found stuff that wasn’t there,” said Steven Salzberg, an expert on analyzing DNA sequences at Johns Hopkins University, who published one of the recent critiques. The authors of the work defended their data and pointed to more recent studies that reached similar conclusions. The unfolding debate reveals the tension between the potentially powerful applications that may come from understanding tumor microbes, and the challenge of deciphering their true nature. Independent experts said the current controversy is an example of the growing pains of a young but promising field. Biologists have known for decades that at least some microbes play a part in cancer. The most striking example is a virus known as HPV, which causes cervical cancer by infecting cells. And certain strains of bacteria drive other cancers in organs such as the intestines and the stomach.
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