Tamoxifen in Ductal Carcinoma In Situ

The widespread adoption of screening mammography has resulted in an increased incidence of ductal carcinoma in situ (DCIS), which now accounts for 20% to 30% of new breast cancer diagnoses. Despite treatment with combined lumpectomy and radiation therapy, up to 15% of women will experience an ipsilateral breast recurrence, with 50% of these recurrences containing invasive disease. There is also a 6% incidence of contralateral breast cancers in women treated for DCIS. The recognition that adjuvant tamoxifen reduces local, regional, and distant disease in women diagnosed with invasive breast cancer led to the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-24 study, which randomized more than 1,800 women undergoing breast-sparing surgery and radiation for DCIS to adjuvant tamoxifen versus placebo for 5 years. At 7 years of follow-up, there was a statistically significant 27% reduction in the annual incidence rate of all breast cancer–related events for those women receiving tamoxifen, including a 48% reduction in invasive breast cancer. The benefit attributable to tamoxifen was confined to those tumors that were estrogen receptor (ER)-positive. However, adverse events, including endometrial cancer, thromboembolic events, and cataracts, are more common in older women. Tamoxifen should be considered as an adjunct to treatment for women undergoing breast-conserving surgery for ER-positive DCIS.