NEW YORK (Reuters Health) – After breast-conserving surgery for invasive cancer, mammographic density is a risk factor for local recurrence, particularly in women who don’t undergo radiotherapy, investigators in Toronto report in the December 15th issue of Cancer.
“We observed a large effect of mammographic density on local disease recurrence, but not on distant recurrence or death,” Dr. Steven A. Narod, at the Women’s College Research Institute, and associates write.
Their study involved 335 women, in whom breast density was classified as low, intermediate or high based on the extent occupied by ductal prominence or dysplasia. Breast density was less than 25% in 99 women, 25% to 50% in 107 women, and greater than 50% in 129. Estrogen receptor status was similar in the 3 groups.
During average follow-up intervals of 7 to 8 years, 34 women (10%) developed local recurrence, including 20 with high-density breasts, 11 with intermediate-density breasts, and 3 with low-density breasts.
Actuarial risks for local disease recurrence at 10 years in the high, intermediate and low density groups were 21%, 13% and 5%, respectively.
On multivariate analysis, compared to the low density group, the hazard ratios for development of local recurrence were 5.7 for the high-density group and 3.6 for the intermediate density group.
The investigators point out, however, that denser breasts increased the recurrence risk only when patients did not have radiotherapy. Among women who did not have postoperative radiation treatment, the actuarial risk of recurrence at 10 years was 40% in the high-density group, whereas there were no recurrences in the low-density breasts (p < 0.01)
In women who did have radiotherapy, the prognostic effect of breast density was “minimal and nonsignificant.”
At present, we have neither a biologic nor a genetic explanation for the association of breast density with risk of recurrence – nor, for that matter, do we fully understand the well known association of density with primary breast cancer risk, the authors said.
Their findings, however, could still have significant clinical implications. “If it could be confirmed that women with low breast density… do not benefit from radiotherapy, this could then result in considerable savings, reduced morbidity, and improved quality of life,” the researchers maintain.
On the other hand, they conclude, “we believe these data confirm the benefit of radiotherapy in women with dense breasts.”