MedWire News: Women who take aspirin on a daily basis are less likely to develop hormone-sensitive breast cancer than those who do not take the drug, US researchers have found.

Dr Gretchen Gierach, from the National Cancer Institute in Rockville, Maryland, and colleagues explain that, in theory, aspirin and other non-steroidal anti-inflammatory drugs may reduce the risk of breast cancer by blocking the action of an enzyme called cyclooxygenase and reducing the amount of the hormone oestrogen that the body produces.

But they add that studies exploring this relationship have produced conflicting results.

To investigate further, the researchers data on the use of non-steroidal anti-inflammatory drugs among more than 127,000 women, aged between 51 and 72 years, who participated in a long-term US health study.

Over the course of the study period, 4501 of the participants developed breast cancer.

The researchers found that, overall, the use of non-steroidal anti-inflammatory drugs was not associated with a reduced risk of breast cancer.

However, further analysis revealed that women who used aspirin on a daily basis for conditions such as cardiovascular disease were 16% less likely than other women to develop a common type of breast cancer that needs the hormone oestrogen to grow, called oestrogen receptor-positive breast cancer.

The use of other non-steroidal anti-inflammatory drugs was not associated with a reduced risk of breast cancer, nor was aspirin linked to a reduced risk of other types of breast tumours.

Dr Gierach and team conclude: "Our results do not support an important influence of non-steroidal anti-inflammatory drugs on total breast cancer risk. Daily aspirin use, however, appeared to offer some protection for oestrogen receptor-positive breast cancer in this population.

They add: "Our results provide support for further evaluating relationships in prospective studies with well-defined measures of non-steroidal anti-inflammatory drug use by non-steroidal anti-inflammatory drug type... and by oestrogen receptor status."

The research is published in the journal Breast Cancer Research.