Jan 4, 2019
Ryan Weight, DO, MS, is an assistant professor in the Department of Medical Oncology at the University of Colorado specializing in the treatment of cutaneous malignancies, including melanoma. He is a member of the Training & Education Working Group.
The human gastrointestinal tract is inhabited by a diverse
population of bacteria that play a crucial role in maintaining
homeostasis both within the gut and within the body. These
various species of bacteria aid in the digestion and absorption
of food products as well as functioning in less obvious roles such
as protecting against invasive gastrointestinal infections and
modulating the body’s natural immune system.
Recent advances in our understanding of the microbiome’s role
in maintaining a balanced immune system has led to the suggestion
that the bacterial makeup of the gut microbiome influences the
effectiveness of immune checkpoint blockade drugs, which stimulate
the immune system to treat cancer.
Research published in the journal Science by Routy et al.
demonstrated that disruption of the gut microbiome through the
use of antibiotics could alter the body’s response to certain immune
checkpoint blockade drugs in patients with lung and kidney cancer.
They went on to show that performing a fecal microbiota transplant
(FMT), the process of transferring feces from one organism to another,
using stool from a human patient with a “favorable” gut microbiota
to a cancer-bearing mouse could effect the response of the mouse’s
tumor to immunotherapy. Similarly, a second article published in
Science by Gopalakrishnan et al. showed that patients undergoing
treatment with immune checkpoint blockade for melanoma were
more likely to respond to treatment if a certain bacterial species
were present within the gut microbiota as well as if a more diverse
bacterial population was present. Again, mice that received FMT
from melanoma patients who responded to treatment had a higher
likelihood of responding to immune checkpoint blockade drugs.
The results from these studies provide insight into the complex
interplay between the body’s immune system and the bacterial
makeup of the gastrointestinal tract. However, it is important to
keep in mind that there are many factors that influence whether a
tumor will respond or will not respond to immunotherapy. These
findings do not suggest that antiobiotics should be avoided while
receiving immunotherapy nor that fecal transplants are necessary
for treatments to succeed. Additional research is needed to
fully understand the effect of the microbiota on cancer and
In my practice I recommend any person undergoing treatment
with immunotherapy maintain a varied and well-balanced diet that
includes leafy green vegetables, which tend to carry healthy bacteria
that can be useful in maintaining a diverse gut microbiome. In the
ever-changing landscape of medicine, there may be a time in the
not-so-distant future when testing of a patient’s feces and medically
manipulating the gut ecosystem will become a part of routine