This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.
Introduction: Ductal carcinoma in situ (DCIS) is a non-invasive breast cancer.
Without treatment, DCIS can progress to invasive breast cancer over time. So, all cases of DCIS are treated.
Results from a randomized clinical trial showed tamoxifen may lower the risk of invasive and non-invasive breast cancer, both in the breast treated for DCIS and in the opposite breast, in women with DCIS who have lumpectomy plus radiation therapy .
The benefits of tamoxifen appeared to be limited to women with estrogen receptor-positive DCIS .
A second randomized clinical trial found tamoxifen did not lower the risk of invasive cancer in the same breast, but did lower the risk in the opposite breast. In contrast, it found tamoxifen lowered the risk of DCIS recurrence in the same breast, but not in the opposite breast .
Learn more about treatment for DCIS.
Study selection criteria: Large randomized clinical trials and meta-analyses.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study Population(number of participants)
Absolute Risk of Invasive Breast Cancer per year(number of cases per 1,000 women)
Relative Risk of Invasive Breast Cancer in Women Taking Tamoxifen Compared to Women Not Taking Tamoxifen, RR (95% CI)
Among Women Not Taking Tamoxifen
Among Women Taking Tamoxifen
Randomized clinical trials
National Surgical Adjuvant Breast and Bowel Project, Protocol B-24 [1-2]
1,799 women with DCIS treated with lumpectomy plus radiation therapy
UK Coordinating Committee on Cancer Research 
1,576 women with DCIS treated with lumpectomy either with or without radiation therapy
Staley et al. 
Breast treated for DCIS: 0.79 (0.62-1.01) Opposite breast: 0.57 (0.39-0.83)
* Relative risk for invasive breast cancer in the breast treated for DCIS. Relative risk for invasive breast cancer in the opposite breast was similar, 0.68 (0.48-0.95). When results for 732 participants were examined by hormone receptor status, relative risks showed benefit only for those with hormone receptor-positive DCIS (no benefit for hormone receptor-negative DCIS).
† Absolute risk was not given. However, there was no difference between rates of invasive breast cancer for women not taking tamoxifen and women taking tamoxifen (9% vs. 9%).
‡ Results for all invasive breast cancers (most breast cancers occurred in the breast treated for DCIS).
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