“No ipsilateral benefit was observed in ER-negative disease, emphasizing that tamoxifen must bind to functional ER to exert its beneficial effect on pre-existing residual tumor cells,” the authors note.
Dr. D. Craig Allred, with Washington University School of Medicine in St. Louis, Missouri, and colleagues explain that the NASBP (National Surgical Adjuvant Breast and Bowel Project) B-24 trial showed that adjuvant tamoxifen reduces subsequent ipsilateral and contralateral breast cancers in women with DCIS after standard therapy — but the trial was begun before hormone receptor status was routinely evaluated in DCIS.
The current study is an analysis of outcomes in 732 of the participants for whom receptor status could be determined retrospectively. Tumors were estrogen receptor-positive in 76% of the women and progesterone receptor-positive in 66%, the report indicates.
Compared to placebo treatment, adjuvant tamoxifen in cases of estrogen receptor-positive DCIS was associated with a significant reduction in risk of ipsilateral breast cancer at 10 years (hazard ratio 0.49; p<0.001), the investigators found. The ipsilateral effect in ER-negative DCIS was not significant (HR 1.06; p=0.87).
Adjuvant tamoxifen had a protective effect against the development of contralateral breast cancer regardless of hormone receptor status, the analysis showed.
Factoring in progesterone receptor status generally did not change the predictive value of estrogen receptor status alone, the authors note.
Overall, Dr. Allred and colleagues conclude, “The use of adjuvant tamoxifen should be considered for patients with DCIS.”
The author of an accompanying editorial, Dr. Monica Morrow of Memorial Sloan-Kettering Cancer Center, New York, sums up the results, saying, “This study allows us to refine our definition of the subgroup of women with DCIS most likely to have a favorable risk/benefit ratio with tamoxifen treatment—namely, premenopausal women with two breasts at risk and ER-positive DCIS.”
However, she adds, “At this point, NSABP B-24 is an old trial, and other options are available to postmenopausal women with DCIS who wish to minimize their risk of future breast cancer events.”