CHICAGO -- Late breast cancer recurrence may be emerging as a new concern in patients participating in a study on tamoxifen versus tamoxifen plus radiotherapy treatment, according to a Canadian expert.

Researchers from Toronto's Princess Margaret Hospital recently showed that the 5-year breast cancer relapse rate was significantly lower in 386 women over age 50 who were treated with the combination of radiation and tamoxifen after lumpectomy, compared with 383 women who were treated with lumpectomy and tamoxifen alone (N. Engl. J. Med. 2004;351:963-70).

"But the 5-year results may not be the whole story," lead investigator Anthony W. Fyles, M.D., reported to colleagues at the annual meeting of the Radiological Society of North America.

A small cohort of the study subjects has been followed now for 8 years, and preliminary data from these 87 women suggest that late relapse rates may be creeping up in both treatment groups, said Dr. Fyles, professor of radiation oncology at the University of Toronto. "It's quite a small number of women, and we need to follow more of them for longer lengths of time, but we are concerned that we are starting to see quite a few more relapses," Dr. Fyles told this newspaper.

The published study showed that at 5 years, the relapse rate was 0.6% in the combination therapy group versus 7.7% in the tamoxifen-only group. But the 8-year data, although still showing a distinct advantage to the combination therapy, reveal increased relapse rates in both of the groups: 3.5% in the combination therapy group, compared with 18% in the tamoxifen-only group, he said.

Of concern in the 8-year follow-up are patients over age 70 with tumor sizes of 1-2 cm. In this group, women who received combination therapy had no relapses. But those who received tamoxifen alone had a relapse rate of 17.6%.

The study design involved treatment with tamoxifen for 5 years, and the sudden increase in relapses could be partly explained by the termination of tamoxifen therapy at the 5-year mark. Dr. Fyles said.

"Now what we do ... is often we add an aromatase inhibitor after patients stop the tamoxifen. We don't know yet whether this reduces the risk of relapse, but the available data on these agents suggest that they will lower the risk of late relapse," for breast cancer patients, Dr. Fyles said at the meeting.