No-biotics for Me!
We don’t fully understand how probiotics affect cancer patient prognosis, so they should be approached with caution – at least for now.
Gemma North | | Opinion
We know that one in eight women will be affected by breast cancer in their lifetime. Though some of these cases can be attributed to genetics, diet, and age, we don’t know the underlying cause for the vast majority of cases. Some speculate that the microbiome – the delicate symbiotic balance of microbes that inhabit the human body – could play a role. We already know that if this balance is lost (dysbiosis) then it can trigger obesity and colon cancer; when the level of Fusobacterium in the human colon hits a certain level, it can trigger the release of pro-inflammatory signals that can prime the tissue for cancer growth (1) Whether this happens in other tissues is less well understood.
The microbiome of normal and malignant breast tissues demonstrate significant differences. Malignant breast tissue is dominated by Enterobacteraceae and Fusobacterium and there’s some evidence that a high fat diet in breast cancer patients could be causing this. Interestingly, it seems that bacteria in the gastrointestinal tract (GI) are able to modulate the activity of distal bacteria – in other words, the composition of the GI controls the composition of other tissues. With this in mind, some have suggested that modulation of the GI microbiome could offer benefits to cancer patients. However, as of today, there’s precious little evidence to support these views.
All of this should be set in context. Probiotics and ‘superfoods’ are becoming increasingly popular, especially in the West, but our understanding of how they might influence treatment and disease outcomes is low. Research in this area is still in its infancy, and there is lack of sufficient evidence to suggest that probiotics have a beneficial effect on cancer patients. There’s some evidence that they might have a role as an anti-cancer agent, chiefly through protecting DNA from damage, modulating the immune system, and suppressing carcinogens produced from bacterial metabolites (2). Other studies suggest that Lactobacillus following chemotherapy or radiotherapy may be of benefit to patients suffering from diarrhoea as a secondary side effect of pelvic malignancies (3)
Yet, other studies show very different outcomes. In fact, probiotics might be dangerous to some patients. A systematic review carried out in 2014 suggested that of 1530 patients, 105 experienced severe, often heterogenic adverse reactions to probiotics, including raised intra-cranial blood pressure, septicaemia, and dysphagia (2). There are a number of ways that probiotics might have adverse effects on patients – not least because they provide an additional potential source of infection in patients with weakened immune systems, but also because they may interact adversely with chemotherapeutic drugs, altering the desired effect. We don’t yet fully understand these effects – which suggests that we need to be extremely diligent when we think about giving probiotics to patients.
Of course, probiotics might also offer a lot of promise. They might help repopulate the gastrointestinal tract following chemotherapy, reducing gastro-intestinal toxicity, and they might also stimulate the immune system to fight tumors. Either way, the jury is clearly out on probiotics. But for now, it’s a no to probiotics from me.
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- M Castellarin et al., “Fusobacterium nucleatum infection is prevalent in human colorectal carcinoma.” Genome Res 20, 22, 299–306 (2012). PMID:22009989
- M Kwa et al.,“The Intestinal Microbiome and Estrogen Receptor–Positive Female Breast Cancer” JNCI J Natl Cancer Inst 22, 108 (2016) PMID: 27107051
- MG Redman et al., “The efficacy and safety of probiotics in people with cancer: a systematic review,” Ann Oncol 25, 1919-29 (2014). PMID: 24618152