Three months ago, I wrote about a report that some kinds of pancreatic cancer seem to be associated with particular infections, and wondered “How many similar stories are out there that we don’t know about yet?” Well, that didn’t take long to start being answered. This recent paper in Science (from a multicenter team: Dana-Farber, Broad, Harvard, Barcelona, Yale) shows a very similar relationship in some colon cancers – Fusobacterium nucleatum is the bacterial species this time, along with a few others that seem to hang along with it.
These species have been noticed as something associated with some colon cancer tissue samples, but this new work shows that things are a lot deeper than that. When you look at metastatic tumors derived from such tissues, the metastases have the same bacteria as the primary tumor. What’s more, it appears that the F. nucleatum cells are actually localized inside the tumor cells themselves (which would certainly account for the stability as they break loose and form metastases).
That’s one big step, but the team goes on to another. When rodents are transplanted with xenograft tumor tissues of this type, antibiotic treatment (metronidazole) actually slows tumor progression. That takes us from the “associated with” situation to the “caused/exacerbated by” one, which is similar to what was seen with the earlier work on pancreatic cancer and Mycoplasma species. And just as in that case, this strongly suggests that any patients with this sort of tumor should be tried out on antibiotic therapy; there would seem to be little to lose and potentially much to gain.
It’s been known for some time that stomach cancer is associated with H. pylori infection and there’s a less-well-known connection between Chlamydia infection and cervical tumors. I think that by now we can definitely add “bacterial infection” to the list of causes of cancer, just as viruses were added years ago. It’s surely not a coincidence that the known examples, when you think about it, are all associated with proximity to a large variety of different bacterial species (the digestive and reproductive tracts). Are there oral/throat cancers that will fall into this category as well? The next question, and one that I’m sure is being worked on right now, is a mechanistic one: how do these infections lead to tumorigenesis? How do the Fusobacteria invade colon tissue cells and survive once they’ve done so, and what are the changes that take place afterwards? I can think of a number of hypotheses, and this isn’t even really my field, so I’m sure that people who are in the area have plenty of experiments to run.