The microbiome is all the rage in scientific circles these days and for good reason. We have better tools for studying the bacteria and viruses that share our bodies. We used to just take a piece of tissue, put it on a petri dish and incubate it for an arbitrary amount of time, and then see what grew out. If we didn’t get all the conditions right, nothing would grow.
Now, we take the tissue and map all the DNA and RNA, then subtract all the human DNA and RNA to see what is left. By definition, the remaining genetic material has to belong to other life forms; i.e., bacteria, viruses, etc. This research approach is leading to interesting findings related to the potential of an altered microbiome causing diseases we have not traditionally thought of as infectious.
Epidemiologic studies have indirectly suggested a breast cancer link with the microbiome. They show that women who take a lot of antibiotics have more breast cancer and more recurrences, presumably because their gut flora has been altered.
There have also been many studies showing that the microbiome of your gut can change how you metabolize estrogen. In fact, a team at Rush University Medical Center is currently recruiting from the Army of Women® for volunteers to participate in a breast cancer microbiome study. The purpose of this study is to categorize the bacteria found in the intestines and how these bacteria metabolize estrogen and other female hormones in women who have never had breast cancer, women who have been diagnosed with breast cancer within the last 5 years, and women who have never had breast cancer but who have a first-degree relative WITH breast cancer. They still need participants! Click here to learn more about participating in this microbiome study and share it with your friends.
Newly reported research in mice suggests that the microbiome may also affect the efficacy of chemotherapy. In one study done in France, researchers found that cyclophosphamide (Cytoxan) altered the bacteria in the guts of mice, triggering an immune response which then was able to also attack cancer cells. The tumors in mice that were germ-free or had been given antibiotics did not respond to the drug! In other words, gut microbes may affect the immune response generated by anticancer drugs.
A second study in mice showed that the microbiome directed both local and systemic inflammation. Romina Goldszmid from the NIH found that germ-free or antibiotic-treated mice responded poorly to immunotherapy and platinum therapy.
More recently, a study was done in mice on anti-tumor immunity in melanoma. The researchers got genetically identical mice from two different labs that had been shown to have different microbiomes. They injected melanoma cells under the skin and found different results in the two strains. One showed a strong immune response with lots of immune cells in the tumors and less tumor growth, while the other had less immune response and more tumor growth. When they kept the mice together in one environment so that their microbiomes would become the same, the tumor results were also the same. Most remarkable was that when they did a fecal transplant from the mice with the good bugs to the ones with the not-so-good bugs, the immune responses became the same!
Obviously, the microbiome affects not only the local immune system, but that of your whole body. This is definitely research to watch. Before we know it, an analysis of stool samples to characterize our microbiomes and whether they are healthy will become part of our regular physical exam. Meanwhile, we need to avoid extra or unnecessary antibiotics and maybe even eat a bit of dirt now and again!