Women who take tamoxifen to prevent breast cancer are getting too much of the drug, according to new evidence.
When researchers in Italy measured 12 biological markers in 105 women who were taking different tamoxifen doses, they found that the standard dose of 20 mg daily did not alter a woman's biochemical profile significantly from that of a 10 mg dose every other day (J Clin Oncol, 1999, 70: 2633-38).
However, the higher doses may be increasing the risk of deep vein thrombosis and hypertrygliceridaeamia (high triglyceride levels).
Two biomarkers, high platelet count and triglyceride concentration, implicated in the risk of deep vein thrombosis and hypertryglicerideaemia, showed a trend towards a dose response relation, suggesting that lowering the dose of tamoxifen might reduce the risk of developing either condition when on the drug. Tamoxifen use has also been associated with an increased risk of endometrial cancer as well a sexual dysfunction. The researchers say that the body's oestrogen receptors can easily reach saturation point, after which higher doses begin to increase risk without conferring any extra benefit.
"The choice of a daily dose of 20 or even higher [for prevention] has come from clinical intuition rather than evidence based studies," says Andre Decensi, the head of the research team, The lower dose did not reduce the drug's anti tumour activity, he added.