Unhealthy microbiome linked to breast, colorectal cancer

Two separate studies have revealed the role played by the gut microbiome in the spread and detection of breast and colorectal cancer respectively. The results come just a couple of months after a worldwide collaboration demonstrated a causal link between the gut microbiome and the immune system’s ability to fight cancer, further suggesting the importance of a healthy gut in combating the disease.

Most breast cancers (65% or more) are hormone receptor positive, which means their growth is fuelled by a hormone — either oestrogen or progesterone. Predicting whether such cancers will spread beyond the breast to other parts of the body is a major challenge, as early metastasis is affected by a variety of factors.

“One of them is having a high level of [immune] cells called macrophages present within the tissue,” said Dr Melanie Rutkowski from the University of Virginia. “There have also been studies that have demonstrated that increased amounts of the structural protein collagen in the tissue and tumour also lead to increased breast cancer metastasis.”

When Dr Rutkowski and her colleagues used powerful antibiotics to disrupt the microbiomes of mice with hormone receptor-positive breast cancer, they found this had dramatic effects in the body, priming the cancer to aggressively spread. The results of their study were published in the journal Cancer Research.

“It resulted in inflammation systemically and within the mammary tissue,” Dr Rutkowski said. “In this inflamed environment, tumour cells were much more able to disseminate from the tissue into the blood and to the lungs, which is a major site for hormone receptor-positive breast cancer to metastasize.

“These findings suggest that having an unhealthy microbiome, and the changes that occur within the tissue that are related to an unhealthy microbiome, may be early predictors of invasive or metastatic breast cancer. Ultimately, based upon these findings, we would speculate that an unhealthy microbiome contributes to increased invasion and a higher incidence of metastatic disease.”

Dr Rutkowski emphasised that antibiotics are not dangerous and should not be avoided by women with breast cancer or anyone who needs them to treat infections; for this study, the antibiotics served only as a simple way to create a long-term imbalance to the microbiome, similar to what individuals may experience with chronically unhealthy microbiomes. The research does, however, suggest that doctors eventually may be able to manipulate the microbiome to benefit patients with breast cancer.

The key takeaway for now, Dr Rutkowski said, is the importance of a healthy microbiome, which can be achieved through a healthy, high-fibre diet, regular exercise and plenty of sleep. “If you do all of those things, in theory, you should have a healthy microbiome. And that, we think, is very much associated with a favourable outcome in the long term for breast cancer.”

The news came just a few days after researchers from Osaka University reported that increases in specific microbiome organisms are linked to the malignancies associated with colorectal cancer, such as intramucosal carcinomas and polypoid adenomas. Their results, published in the journal Nature Medicine, reveal that these specific markers could help distinguish cases of colorectal cancer from healthy samples.

Colorectal cancer, the third most prevalent cancer globally, is a relatively slow-moving disease — meaning it takes a long period of time before reaching its final, fatal stages. Therefore, early detection is crucial to ensuring effective treatment.

Recent studies have shown that assessing the genetic changes in faecal samples can accurately reflect the status of the gut microbiome, and may be useful for the early diagnosis of diseases. Seeking to test their theory that colorectal cancer is in part a microbial disease, the Osaka researchers assessed the faecal samples from over 600 patients who underwent colonoscopy, looking to assess the characteristics of their gut microbiota and how they relate to colorectal cancer.

“Our results show that changes in the gut microbiome are present at the very early stages of colorectal cancer development, which could potentially provide vital diagnostic and causative clues for this disease,” said Shinichi Yachida, a corresponding author on the study.

Another corresponding author, Takuji Yamada, added, “Our results revealed that colorectal cancer was linked to an increase in certain factors in the gut microbiome, as well as the presence of cancer-associated organisms. Future studies will focus on the relationship between the gut microbiome and tumour characteristics in individual patients with colorectal cancer. This will help us understand the roles of the microbiome in the development of colorectal cancer.”

Image credit: ©stock.adobe.com/au/peshkova

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