For patients with “good-risk” ductal carcinoma in situ (DCIS) who underwent breast-conserving surgery and did not receive radiotherapy, tamoxifen significantly decreased the risk of recurrence in the same breast, according to results presented at the San Antonio Breast Cancer Symposium (SABCS), held December 10-13, 2024.

“Good-risk” DCIS was defined as grade 1 or 2, 2.5 cm or smaller, and having clear surgical margins of 3 mm or greater.

Current guidelines from the National Comprehensive Cancer Network (NCCN) advise that patients who undergo breast-conserving surgery after a diagnosis of hormone receptor-positive DCIS consider tamoxifen after surgery, whether or not they concurrently receive radiotherapy. However, many factors, including a patient’s individualized risk of recurrence, can influence which therapy options they prefer to pursue.

“The more information we can provide patients about the impact of specific treatments, the more we can empower patients to make choices that are right for them,” said Jean L. Wright, MD, chair of the Department of Radiation Oncology at the University of North Carolina and the Lineberger Comprehensive Cancer Center in Chapel Hill. “I believe that being able to provide clear information to our patients leads to the best care.”

Wright and colleagues combined the data from two clinical trials to evaluate outcomes in patients with DCIS treated with or without radiotherapy. In NRG/RTOG 9804, patients with “good-risk” DCIS were randomly assigned to receive radiotherapy or no radiotherapy. In ECOG-ACRIN E5194, researchers examined the outcomes of patients with both higher-risk and “good-risk” DCIS who did not receive radiotherapy. In both studies, all patients were permitted to take tamoxifen, if desired.

Wright and colleagues, including NRG/RTOG 9804 principal investigator Beryl McCormick, MD, a radiation oncologist at Memorial Sloan Kettering Cancer Center, sought to assess the efficacy of tamoxifen in preventing disease recurrence in patients from both trials who did not receive adjuvant radiotherapy. They analyzed results from 878 patients, 43% of whom received adjuvant tamoxifen. After a median follow-up of almost 15 years, 117 cases of ipsilateral (same breast) recurrence were diagnosed.

The estimated 15-year risk of ipsilateral recurrence was 11.4% for patients treated with tamoxifen and 19% for patients who did not receive tamoxifen, a statistically significant difference. When the data were analyzed by the type of recurrence, tamoxifen use was significantly associated with a decreased rate of ipsilateral invasive breast cancer but was not associated with a significant difference in the rate of ipsilateral DCIS recurrence.

Because the researchers noted that the size of the primary DCIS was significantly associated with the risk of ipsilateral recurrence, they adjusted for tumor size and found that tamoxifen was independently associated with reduced recurrence. When adjusted for DCIS size, patients who received tamoxifen were 44% less likely to experience an ipsilateral recurrence than patients who did not receive tamoxifen.

Similarly, because the grade of the primary DCIS was significantly associated with the risk of an invasive ipsilateral recurrence, they adjusted for DCIS grade and found that tamoxifen was independently associated with reduced invasive recurrence. When adjusted for DCIS grade, patients who received tamoxifen were 51% less likely to experience an invasive ipsilateral recurrence than patients who did not receive tamoxifen.

Wright noted that the risk of an invasive recurrence is among the most important factors when considering adjuvant therapy options. “Previously available data were conflicting about how much impact tamoxifen had on invasive versus DCIS recurrences in patients with favorable prognostic factors, so this finding, in such a robust data set, is clarifying,” she said.

Wright further emphasized that knowing the risk of recurrence, with and without tamoxifen, for patients who choose to forgo radiotherapy can help patients most effectively weigh the risks and benefits of different adjuvant treatment options. “Tamoxifen, radiation, or both, as well as the omission of any adjuvant therapy, are all reasonable options,” she said. “Now, we have more data to help our patients choose among these.”

Limitations of this study include a lack of information about genomic indicators of prognosis, which are used with an increasing frequency to stratify patients with high versus low risk of progression. Further, the data was gathered exclusively from patients who fit a narrow set of criteria for “good risk,” and more data may be necessary to evaluate these findings in patients with different DCIS characteristics.

Funding for this study was provided by grants to NRG Oncology and ECOG-ACRIN from the National Cancer Institute of the National Institutes of Health. Wright declares no conflicts of interest.

This news release was published by the American Association for Cancer Research on December 12, 2024.

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