Among women who have estrogen receptor-positive ductal carcinoma in situ (DCIS) of the breast, adjuvant (post-surgery) treatment with tamoxifen may reduce the risk of subsequent breast cancer. These results were published in the Journal of Clinical Oncology.
DCIS refers to abnormal cells in the lining of a breast duct. It is classified as Stage 0 breast cancer—the earliest possible stage. The condition usually does not produce any symptoms (such as a breast lump), and it was an uncommon diagnosis prior to the introduction of screening mammography. Diagnoses increased greatly once mammography became widespread, and DCIS now accounts for up to one-quarter of all breast cancer diagnoses in the United States.
Treatment of DCIS generally involves either a lumpectomy (removal of the abnormal area of the breast) or a mastectomy (removal of the entire breast). When DCIS is treated with lumpectomy, additional treatment with radiation therapy can reduce the risk of cancer recurrence.
Tamoxifen is a hormonal therapy that interferes with the effects of estrogen. It is commonly used in the treatment of hormone receptor-positive invasive breast cancer, and is also used to reduce the risk of breast cancer in women at high risk of the disease.
The role of tamoxifen among women with DCIS was evaluated in a clinical trial known as NSABP B-24. All women in the study had DCIS that was treated with lumpectomy and radiation therapy. Half the women were given tamoxifen and half were given a placebo. The primary results from the study (published in 1999) indicated that tamoxifen reduced the risk of another breast cancer diagnosis.
In the original study, researchers did not routinely collect or analyze information about the hormone receptor status of the DCIS. The benefits from tamoxifen, however, may vary depending on whether the DCIS was estrogen receptor-positive and/or progesterone receptor-positive.
To explore the relationship between the hormone receptor status of the DCIS and the effects of tamoxifen, researchers analyzed a subset of the women who had participated in the NSABP B-24 study. Information about estrogen receptor status and progesterone receptor status was available for 732 of the original 1,804 study participants. Roughly three-quarters of these women had DCIS that was estrogen receptor-positive.
- Among women with estrogen receptor-positive DCIS, treatment with tamoxifen substantially reduced the likelihood of another breast cancer.
- Among women with estrogen receptor-negative DCIS, the benefits provided by tamoxifen were not statistically significant, suggesting that they could have occurred by chance alone. The relatively small number of women with estrogen receptor-negative DCIS, however, makes it difficult to draw definitive conclusions about the effects of tamoxifen in this group.
These results suggest that adjuvant tamoxifen may benefit women with estrogen receptor-positive DCIS.
 Kerlikowske K. Epidemiology of ductal carcinoma in situ. Journal of the National Cancer Institute Monographs. 2010;41:139-41.
 Allred DC, Anderson SJ, Paik S et al. Adjuvant tamoxifen reduces subsequent breast cancer in women with estrogen receptor-positive ductal carcinoma in situ: a study based on NSABP protocol B-24. Journal of Clinical Oncology. Early online publication March 5, 2012.