The breast cancer drug tamoxifen may cause birth defects.

Specialists from the University of California report on a case of a 35 year old woman, taking 20 mg of tamoxifen a day, who gave birth to a baby girl born with genital abnormalities.

The woman, who died two weeks after the birth, had stopped taking the drug after the fifth month of pregnancy.

Animal experiments have shown some link between the drug and the development of the genitals, but this has never been substantiated in trials among humans. One, involving 85 women who became pregnant while taking the drug as a protection against breast cancer, reported no defects at birth, although it did not state if the women had taken the drug during the first 20 weeks of pregnancy.

The picture may become clearer eventually as more and more women delay pregnancy until they are older, and so are more likely to be taking tamoxifen at the same time (Lancet, 1997; 350: 183).

Tamoxifen may trigger hypertriglyceridemia (high fat levels) in women who have a history of the condition, doctors warn. Three cases of severe hypertriglyceridemia, caused by the drug, were reported in women who had the condition previously. One died, but the other two recovered when the drug was withdrawn (New Engl J Med, 1997; 337: 281).

For more information see the newly revised WDDTY Guide to Cancer.