Tumors carry their own bacteria signature

Researchers at the Weizmann Institute of Science analyzed 1,526 tumors and their surrounding tissue across seven cancer types and found that nearly every tumor type carried a distinct, consistent set of resident bacteria.

Deborah Nejman and Ravid Straussman's team combined gene sequencing with microscopy and culturing to confirm the microbes sat inside tumor cells, not on the surface as contamination. Detection ranged from about 14 percent of melanoma samples to more than 60 percent of breast, pancreatic, and bone tumors, with bacteria found mostly inside cancer and nearby immune cells.

Breast tumors carried the richest and most varied bacterial population of the seven types studied. Some bacterial signatures lined up with patient smoking history and with how well a tumor responded to immunotherapy, suggesting these microbes might influence treatment outcomes rather than just riding along passively. Whether the bacteria cause any of these effects, or simply reflect them, is still being worked out.

Tumors are not sterile growths after all.