Gut Microbiome: Link Between Smoking and Cancer?

Although there's no doubt that smoking causes cancer and worsens cancer outcomes, exactly how it causes or worsens cancer remains uncertain. Now, a study in mice suggests that alterations in the intestinal microbiome may play a role.

Animals with intact gut microbiome who received cancer cell implants showed accelerated tumor progression following exposure to cigarette smoke, but this acceleration was not seen in similar mice whose microbiomes had been obliterated with antibiotics, said Prateek Sharma, MBBS, of the University of Miami in Florida.

Sharma described the research in a press briefing organized by Digestive Disease Week (DDW), the annual meeting that was cancelled this year because of COVID-19.

He also reported that, when the same experiment was repeated in Rag1-/- mice -- engineered to lack adaptive immune function -- tumor responses to cigarette smoke did not differ according to microbiome status. That, he said, suggests the adaptive immune system mediates the connection between the microbiome and cancer growth.

"If the same relationship is found in human studies, treatments that modify the gut microbiome could improve cancer outcomes for smokers, who are susceptible to many cancers and fare worse in cancer treatment," Sharma said in a DDW press release.

Such a treatment could be as simple as "selective" antibiotic or probiotic therapy, he said, although the gut microbiome is important for a wide variety of normal functions and its alteration could have unforeseen consequences.

Numerous previous studies have connected smoking to alterations in the human gut microbiome; one study presented late last year showed that smoking cessation does as well.

At the DDW press briefing, Sharma said future research should include closer examination of "what changes smoking brings to the gut microbiome": which bacteria are enhanced and which are depleted, for example. At the top of the agenda, however, is "definitely proving whether this phenomenon holds true for humans," he said.

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