Dense Breasts at Higher Risk of Cancer Recurrence

Breast cancer patients with dense breasts may be more likely to see their disease return after lumpectomy, researchers found.

High mammographic density was associated with a nearly six-fold higher recurrence rate after breast conserving surgery (21% versus 5% at 10 years, P=0.006), Steven A. Narod, MD, Women's College Hospital in Toronto, and colleagues reported online in Cancer.

But radiation therapy appeared to eliminate the disadvantage, the researchers said.

Although exercise and hormone therapy can alter the relative proportion of dense tissue in the breast, it's not clear whether these measures would impact the risk of breast cancer recurrence, they cautioned.

Prior studies have also shown up to six-fold higher breast cancer incidence for women with the most dense breasts despite lower mammographic sensitivity in this group.

The mechanism could be that denser breasts have more circulating growth factors, the researchers said, but "the biological basis of the association with cancer risk is largely unknown."

So to see if the association extended to recurrence as well, Narod's group reviewed outcomes for 335 women who received breast conserving surgery for invasive breast cancer at their center over an 11 year period and who had a pretreatment mammogram available for assessment of breast density.

Overall, 107 women had intermediate-density breasts with dysplasia or ductal prominence occupying 25% to 50% of the breast.

The 129 women with more than 50% dense tissue in the breast tended to be younger and were less likely to be postmenopausal than others.

This high mammographic density group also had the highest rate of local recurrence of breast cancer (15.5% versus 10.3% intermediate and 3% low density).

But even after controlling for age, menopausal status, and adjuvant radiotherapy use, the 10-year actuarial risk of local recurrence was 5.7 times higher for the high-density group compared with those who had less than 25% mammographic density (21% versus 5%, P=0.006).

The intermediate-density group had a 3.6-fold higher local recurrence risk than the low-density group as well (10-year actuarial rate 13% versus 5%, P=0.05).

The protective effect of having been treated with radiotherapy was similar regardless of mammographic density (P=0.57), but women who did not get this treatment were substantially more likely to see their disease return if their breasts were dense (10-year rate 40% for high versus 0% for low density, P<0.0001).

"We believe these data confirm the benefit of radiotherapy in women with dense breasts," the researchers wrote.

Another implication of this finding is that women with low-density breasts may be able to safely avoid radiation given the lack of recurrences. However, Narod's group cautioned that the small study was only hypothesis generating in this regard.

Mammographic density did not appear correlated with metastasis to distant sites.

The study was supported by the the Canadian Breast Cancer Foundation.

The researchers reported no conflicts of interest.

Primary source: Cancer Source reference: Tulin C, et al "Mammographic density and the risk of breast cancer recurrence after breast-conserving surgery" Cancer 2009; 115.