Five years of tamoxifen in postmenopausal women with early breast cancer appears to reduce mortality due to coronary heart disease by more than 30% compared with women who remain on the drug for just 2 years, Swedish researchers report.

The results come from continued long-term follow-up of women who participated in the landmark tamoxifen study by the Swedish Breast Cancer Group. Dr. Bo Nordenskjold, head of the Oncology Centre for Southeast Sweden, and co-investigators reported in 1996 that 5 years of tamoxifen treatment improved survival in postmenopausal women with early breast cancer compared with those who received 2 years of treatment.

In the follow-up involving 4175 women for another 5 years, Dr. Nordenskjold and his colleagues found that among the women who took tamoxifen for 2 years, 381 women died from causes other than breast cancer, compared with 307 non-breast cancer deaths in the 5-year group.

At a press briefing Monday at the 29th European Society of Medical Oncology Congress, he said the major difference was cardiovascular mortality and coronary heart disease. In the 2-year arm, 163 women died from cardiovascular disease, compared with 136 women in the 5-year arm. In the 2-year arm, 78 women died from coronary heart disease compared to 54 deaths among women in the 5-year arm.

The effect on coronary heart disease, however, is delayed.

“This difference in mortality in coronary heart disease is a late event,” Dr. Nordenskjold said. “The first 7 or 8 years you see no difference. But the difference emerges gradually.”

In a statement commenting on the report, Professor Monica Castiglione from the International Breast Cancer Study Group, Bern, Switzerland, said, “Dr. Nordenskjold and colleagues are reporting very mature data from a trial started more than 20 years ago. The trial reported earlier results in 1996, showing the superiority of 5 years of tamoxifen over 2 years in terms of breast-cancer-event-free survival, overall survival, contralateral breast cancer incidence, and increase of endometrial cancer cases. These observations have now been confirmed.”

“In the current presentation the authors report a reduction in mortality from coronary heart disease with the prolonged use of tamoxifen,” she continued. “A similar observation had already been made by the Scottish Group (comparing tamoxifen postoperative versus tamoxifen at relapse) for myocardial infarction.”

“It is interesting that in the present report, no significant increase in thromboembolic events could be observed with the prolonged use of tamoxifen,” Dr. Castiglione pointed out, “whereas in the Scottish trial, tamoxifen-treated patients showed a significantly higher incidence of thromboembolism when compared to an untreated control group.”