Blueberries contain numerous chemopreventive compounds, among them pterostilbene, resveratrol, and various anthocyanins (delphinidin, cyanidin, malvidin, peonidin, and petunidin). Pterostilbene, for example, has been shown to reduce obesity-related breast cancer cell growth and proliferation and to increase the effectiveness of tamoxifen in hormone receptor positive (ER+/PR+) breast cancer cells. Pterostilbene can also inhibit the formation of breast cancer stem cells and reduce their metastatic activities.

Blueberries have been shown to inhibit both hormone receptor positive (ER+/PR+) and hormone receptor negative (ER-/PR-) breast cancer cell growth. Blueberry diets have also been shown to reduce mammary tumor development in animal models of breast cancer. Now a new study has reported that whole blueberry powder reduces both mammary tumor growth and metastasis in a rodent model of triple negative breast cancer under conditions of systemic inflammation.

Blueberries inhibit triple negative breast cancer growth and metastasis

Triple negative is a subtype of breast cancer that is estrogen receptor negative (ER-), progesterone receptor negative (PR-), and human epidermal growth factor receptor 2 negative (HER2-). Blueberry extract has been shown to exhibit antitumor activity against MDA-MB-231 triple negative breast cancer cells and reduce their metastatic potential. Blueberry was found to inhibit cell proliferation in triple negative cells with no effect on normal breast cells in one study. Blueberry also reduced the metastatic potential of triple negative cells through inhibition of cell motility.

In animal studies, dietary blueberry has been shown to reduce triple negative tumor volume in female mice. Blueberry diets reduced triple negative proliferation (as measured by Ki-67) and increased cell death. In addition, a blueberry diet inhibited triple negative tumor metastasis in another mouse study. Analysis of tumor tissues has demonstrated that blueberry-fed mice tumors have significantly altered expression of genes important to inflammation, cancer, and metastasis.

Latest research finds blueberry reduces tumor burden and metastasis

The study referenced at the beginning of this news story was designed to investigate the inhibitory effect of blueberries on triple negative breast cancer under conditions of systemic inflammation. Breast cancer growth, invasion and metastasis all are promoted by inflammation. The authors also sought to identify the mechanism of action underlying the effects of blueberry on inflammatory proteins. To conduct the study, the authors used female mice bearing tumors grown from human MDA-MB-231 triple negative breast cancer cells. A proinflammatory microenvironment was induced by feeding the mice a high-fat Western diet. One group of mice was also fed whole blueberry powder (5% of total diet). The remaining mice (acting as controls) were given the Western diet without blueberry powder. Tumor formation and metastasis was then studied in both groups of mice.

Mice given the blueberry diet were found to have smaller tumors, less ulceration, and significantly less metastasis to nearby lymph nodes than mice fed the Western diet without whole blueberry powder. Circulating levels of specific anti-inflammatory cytokines (small signaling molecules used in intercellular communication) were increased and specific cytokine expression was altered in the blueberry group. The authors conclude that blueberries may inhibit triple negative breast cancer growth and related metastasis by reducing inflammation by means of specific cytokine-driven pathways.

Please see our article on what triple negative patients and survivors should eat for more information.