High daily intakes of coffee were found to be associated with a statistically significant decrease in the risk of oestrogen receptor negative (ER negative) breast cancers, concludes a joint Swedish and Singapore abstract presented at the 12th International Breast Cancer Conference (St Gallen, Switzerland, 16 -19 March). Coffee, the authors say, is likely to affect the different biological breast cancer subtypes in different ways.

While previous studies have suggested that high coffee consumption is associated with a modest reduction in breast cancer risk, a meta-analysis of over 500 papers relating the consumption of coffee to cancer in various sites reported a null association with breast cancer risk. "But the complex make-up of chemicals in coffee may differentially affect breast cancer of different oestrogen subtypes," explained Jingmei Li, the first author of the study.

For example, trigonelline, a phytoestrogen present in coffee extract, has been suggested to activate oestrogen receptors through an oestrogen-independent mechanism, and is capable of stimulating cell growth of an ER-positive cell line at low concentrations. In addition, coffee has been shown to significantly contribute to levels of plasma enterolactone, a different phytoestrogen associated with a decrease in ER-negative breast cancer risk.

In the current study Li and colleagues from the Karolinska Institute (Stockholm, Sweden) and Genome Institute of Singapore, explored the association between coffee consumption and breast cancer (stratified according to oestrogen receptor tumour subtypes) among 2,818 cases of breast cancer and 3,111 controls.

In the stratified case-control analysis the investigators found that the incidence of oestrogen receptor positive breast cancer was 66% less likely to occur among women who drank more than five cups of coffee a day in comparison to those who drank less than one cup. "We found no evidence that coffee consumption increases the overall risk of postmenopausal breast cancer. However, a high daily intake of coffee was found to be associated with a significant decrease in ER-negative breast cancer among postmenopausal women," said Li, from the Karolinska Institutet, Sweden, adding that further studies are needed to confirm the effects of coffee consumption according to breast cancer subtypes.

Reference

J Li, K Humphreys, K Czene et al. Coffee consumption modifies risk of oestrogen-receptor negative breast cancer Abstract number P 150