Some researchers believe that the gut flora influences the development of certain cancers, and that probiotics may have a role in preventing or managing those cancers. Where is the research headed next? Learn more here.
Probiotics & Cancer
Cancer is among the richest and most contentious fields of medical research, and the potential role of probiotics is intriguing. However, because many cancer patients undergo treatments that suppress their immune systems, the role and safety of probiotic supplementation in cancer patients is unclear. Thus, it’s especially important to talk to your doctor before starting a new probiotic if you are undergoing cancer treatment.
Cancer Research: Insufficient Evidence for Any Benefit
Probiotic bacteria have shown antitumor activities, and some studies suggest they could potentially reduce the incidence of cancer. Some researchers believe that they may delay cancer onset and progression as well as regulate cell growth mechanisms [1].
However, the purported anticancer benefits of probiotics are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of probiotics for either the prevention or treatment of cancer. Remember to speak with a doctor before taking probiotic supplements, and never use it in place of something your doctor recommends or prescribes.
Studies in Humans
Consumption of soy isoflavones in combination with L. casei decreased the risk of breast cancer among Japanese women [2].
L. casei administration significantly reduced the recurrence rate of bladder cancer and colorectal cancer in cancer patients [3].
Animal Studies
Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
L. rhamnosus decreased the incidence of colon tumors and precancerous lesions in experimental animals as well as in human cells [1]. This species also demonstrated antitumor effects in animal models of bladder cancer [4].
L. plantarum enhanced the anti-tumor immune response and delayed tumor formation in mice with intestinal adenocarcinoma [5] and exhibited anti-colorectal cancer activities [6].
Long-term administration of L. plantarum suppressed breast cancer in rats [7, 8] and inhibited the development of rat colon carcinogenesis [9].
L. casei decreased cell migration and invasion of colorectal cancer cells [10, 11], inhibited human and mouse colon cancer cell growth, and resulted in an 80% reduction in tumor volume of treated mice [12].
L. casei delayed and suppressed tumor growth in mice with breast cancer, both when it was administered preventively and as a treatment. L. casei further reduced tumor vascularity and lung metastasis and prolonged survival [13, 14, 15].
Similarly, L. casei decreased breast tumor volume and tumor vascularity in rats [2].
L. salivarius suppressed colon carcinogenesis [16] and inhibited oral cancer growth in rats [17].
L. delbrueckii ssp. bulgaricus inhibited intestinal carcinogenesis in rats, ear-duct tumors in rats, and tracheal carcinogenesis in hamsters [18]. This probiotic was also reported to inhibit the growth of sarcoma [19], leukemia, plasmacytoma, adenocarcinoma, melanosarcoma, and spontaneous tumors in mice [20].
L. acidophilus altered the cytokine production in tumor-bearing mice into a Th1 protective pattern, favorable to anti-tumor immunity [21].
L. acidophilus suppressed colon tumor incidence, tumor multiplicity, and reduced tumor size in mice [22].
Oral administration of L. acidophilus increased mouse survival [23], decreased tumor growth and increased lymphocyte proliferation in mice with breast tumors [21].
L. acidophilus reduced tumor volume growth by 50.3 %, reduced the severity of colonic carcinogenesis, and enhanced cancer cell death in mice [24].
L. helveticus inhibited the development of fibrosarcoma [25] and delayed the development of breast tumors in mice [25].
Dietary B. longum significantly inhibited colon and liver and small intestinal tumors in male rats. In female rats, dietary supplementation also suppressed mammary carcinogenesis [26].
L. longum inhibited colorectal tumors in mice [27] and rats [28, 29].
B. animalis ssp. lactis decreased the mean number and size of tumors in mice with colitis-associated cancer [30].
The synbiotic combination of carbohydrate ‘resistant starch‘ and B. animalis ssp. lactis protected against the development of colorectal cancer (CRC) in rats [31, 32].
Heat-inactivated C. butyricum displayed antitumor activity against sarcoma in mice [33] and inhibited the metastasis of melanoma, possibly by stimulating natural killer (NK) cell cytotoxic activity [34].
Furthermore, in mice, co-treatment with C. butyricum and B. subtilis inhibited the development of colorectal cancer [35].
An antitumor molecule derived from L. brevis inhibited colon adenocarcinoma cell viability and the growth of these cells in mice [36].
Mice with fibrosarcoma that were treated by S. thermophilus were protected against this tumor when re-challenged. Additionally, spleen T-lymphocytes from cured animals could effectively transfer the antitumor activity to recipients transplanted with the tumor [37].
P. freudenreichii killed colon cancer cells in rats [38].
Takeaway
Some researchers suspect a link between gut microbiota and cancer development. Though human studies are scarce, some early clinial research indicates a possible link between probiotic supplementation and reduced rates of breast, bladder, and colorectal cancers. Animal research has thus far supported this hypothesis as well, with a significant reduction in cancer rates in animals given probiotic supplements.
Future research will clarify the role, if any, of probiotics to support cancer therapies. Given that many cancer patients are immunosuppressed, it is especially important to talk to your doctor before taking probiotics during chemotherapy or other cancer treatments.
Further Reading
We’ve compiled deep dives into each potential benefit of probiotics. Check them out here:
