Blueberries may reduce the growth of breast cancer! So screamed newspaper headlines. A bit of an overstatement. The study referred to was carried out on female nude mice. These are mice specially bred for laboratory research that derive from a strain with a genetic mutation that causes them to have an under-active thymus gland resulting in an impaired immune system. Outwardly they lack body hair, hence the nickname “nude”. Suffice it to say that these nude mice are not a perfect model for predicting biological effects even in other mice, never mind in humans. Still, they are valuable in research because cancer cells can be introduced without a rejection response. And the blueberry study was all about mice being injected with breast cancer cells.
But these were very specific breast cancer cells, known as “triple negative cells.” The “triple negative” refers to the fact the growth of these cells is not supported by the hormones estrogen or progesterone and that they also test negative for the presence of “human epidermal growth factor receptor 2 (HER2),” a protein that promotes the growth of cancer cells. “Triple negative cells” therefore do not respond to standard hormone blocking drugs such as tamoxifen or to medications like herceptin that interfere with the HER2 receptor. Triple negative cells are very aggressive, but are the cause of only 15% of all breast cancers. Researchers at City of Hope Hospital in Los Angeles treated nude mice to a diet that included either 5% or 10% blueberry powder by weight. After two weeks, the mice were injected with the triple negative breast cancer cells. A control group of animals was fed in the same fashion but without the blueberry powder. Why undertake such an experiment? Because earlier laboratory studies had shown that blueberry extract had “anti-angiogenesis” activity, meaning that it interfered with the formation of blood vessels that tumours need to grow. After six weeks, the mice fed the 5% blueberry diet had a tumour volume that was 75% lower than the control animals, but strangely, those fed the higher dose blueberry diet showed only a 60% lower tumour volume. In terms of human equivalents, the 5% blueberry diet corresponds roughly to eating about two cups of fresh blueberries a day. In a second study, the blueberry-fed mice exhibited a reduced risk of the cancer spreading to other parts of their body.
What then would be a realistic headline to describe these results? How about, “Large daily dose of blueberry powder may reduce the growth of a rare type of artificially induced breast cancer in a special variety of immune suppressed mouse?” Wouldn’t sell many papers, one would guess. And what do these mouse experiments mean for humans in terms of preventing or treating breast cancer? Not much. All we can do is mutter that blueberry extracts “warrant further investigation.”