The risk of developing blood clots while undergoing breast cancer therapy can be dramatically increased due to a gene found mostly in women of Scandinavian origin, according to research.
Scientists have found that patients treated with breast cancer drug tamoxifen are five times more likely to develop blood clots if they had the Factor V Leiden (FVL) gene.
Conditions that can occur as a result of the blood clot include deep vein thrombosis and pulmonary embolism, a potentially fatal clot on the lung.
FVL, which is passed down through families, is most common among people of Scandinavian or northern European ancestry, and around 5% of the UK population have the mutation.
Previous studies have shown that tamoxifen doubles the risk of a blood clot, or thromboembolism, in women overall.
The new research shows that it has a much bigger impact on patients with FVL.
Scientists in the US looked at 412 women who were treated with tamoxifen after undergoing surgery for breast cancer.
A total of 141 of the women, whose mid-range age was 64, developed blood clots.
The researchers, led by Dr Judy Garber, from the Dana-Farber Cancer Institute in Boston, wrote in The Journal of the National Cancer Institute: “These data may prove useful to women who must decide between tamoxifen and an effective, essentially non-thrombogenic, alternative adjuvant therapy for breast cancer.”