Coffee inhibits the growth of tumors and reduces the risk of recurrence in women with breast cancer and treated with the drug tamoxifen, confirmed a new study published in Clinical Cancer Research (2015; doi:10.1158/1078-0432.CCR-14-1748).

A number of research studies have shown that coffee helps to protect against breast cancer. This study, which is a follow-up of the results the researchers obtained 2 years ago, was carried out at Lund University and Skåne University Hospital in Sweden, in collaboration with researchers in the United Kingdom.

“Now, unlike in the previous study, we have combined information about the patients’ lifestyle and clinical data from 1,090 breast cancer patients with studies on breast cancer cells. The study shows that among the more than 500 women treated with tamoxifen, those who had drunk at least two cups of coffee a day had only half the risk of recurrence of those who drank less coffee or none at all,” explained researchers Ann Rosendahl, PhD, and Helena Jernström, PhD, who obtained the results in collaboration with Jeff Holly, PhD, and his research team at University of Bristol.

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“The study also shows that those who drank at least two cups of coffee a day had smaller tumors and a lower proportion of hormone-dependent tumors. We saw that this was already the case at the time of diagnosis,” said Rosendahl and Jernström.

In the cell study, the researchers looked more closely at two substances that usually occur in the coffee drunk in Sweden: caffeine and caffeic acid.

The researchers explained that the breast cancer cells reacted to these substances, especially caffeine, with reduced cell division and increased cell death, especially in combination with tamoxifen. They explained that this shows that these substances have an effect on breast cancer cells and turn off signalling pathways that the cancer cells require to grow.

The researchers have demonstrated both in breast cancer patients and at the cellular level that coffee appears to reinforce the effect of treatment with tamoxifen, but emphasize the importance of taking prescribed medication.

“They are incredibly important, but if you like coffee and are also taking tamoxifen, there is no reason to stop drinking it. Just two cups a day is sufficient to make a difference,” said the researchers.