Two recent studies have reported new insights into the role of the tumor-associated microbiome in both drug response and metastasis. Researchers working at the Fred Hutchinson Cancer Center, Seattle, reported in the Nov. 16, 2022, issue of Nature that bacteria can promote the spreading of cancer as single cells with recruitment of myeloid host cells. In a parallel publication, the same team reported in the Nov. 15, 2022, issue of Cell Reports that the primary chemotherapy used to treat colorectal cancer (CRC), 5-fluorouracil (5-FU), was less effective when the tumor included bacteria that were insensitive to 5-FU antimicrobial activity.