Women with dense breasts who have had lumpectomies for breast cancer are at a higher risk of a recurrence, according to a new study.

However, the increased risk is for recurrences near the original cancer. The higher risk was also only seen in women who were not treated with radiation after their surgeries.

And breast density does not seem to have an effect on the risk that the disease will spread or the chance of survival, researchers report in the journal Cancer.

Women with dense breasts are known to be at increased risk of breast cancer, but it was unclear whether they were at a higher risk of a recurrence once they had been treated. It is also unclear why breast density should have any effect on risk.

Dr. Steven A. Narod, at the Women’s College Research Institute, and colleagues studied 335 women, in whom breast density was classified as low, intermediate or high.

About one in ten of the women developed a recurrence of cancer during the time the researchers studied, about eight years: 20 with high-density breasts, 11 with intermediate-density breasts, and 3 with low-density breasts.

That meant that at ten years, women in the high, intermediate and low density groups had a 21 percent, 13 percent and 5 percent risk of recurrence, respectively.

The investigators point out, however, that denser breasts increased the recurrence risk only when patients did not have radiation treatments.

Among women who did not have postoperative radiation treatment, the risk of recurrence at 10 years was 40% in the high-density group, while there were no recurrences in the low-density breasts.

The findings, write the authors, confirm the benefit of radiation therapy in women with dense breasts.

SOURCE: Cancer, 2009.