Adjuvant use of tamoxifen is associated with a big drop in the risk of recurrence in the same breast among patients with “good-risk” ductal carcinoma in situ (DCIS) after breast-conserving surgery without radiotherapy.

In an exploratory analysis combining NRG/RTOG 9804 and ECOG-ACRIN E5194 trials, the 15-year estimate of ipsilateral breast recurrence (IBR) was significantly lower among patients who received tamoxifen than among those who did not (11.4 percent vs 19.0 percent; hazard ratio [HR], 0.52, 95 percent confidence interval [CI], 0.35?0.77; p=0.001). [SABCS 2024, abstract SESS-3482]

When stratified by recurrence type, tamoxifen use was associated with a significant reduction in invasive IBR (6.0 percent vs 11.5 percent; HR, 0.47, 95 percent CI, 0.27?0.80; p=0.005) but not DCIS IBR (5.5 percent vs 8.1 percent; HR, 0.61, 95 percent CI, 0.34?1.08; p=0.09).A nonsignificant decrease in contralateral breast events was also seen with tamoxifen use (5.6 percent vs 8.8 percent; HR, 0.68, 95 percent CI, 0.39?1.18; p=0.17).

In multivariable Fine-Gray regression analysis for IBR, DCIS grade fell out of the model and despite adjusting for tumour size, tamoxifen use remained significantly associated with reduced IBR (HR, 0.56, 95 percent CI, 0.38?0.84; p=0.0044).

According to lead study author Dr Jean Wright from the University of North Carolina in Chapel Hill, North Carolina, US, the risk of an invasive recurrence is among the most important factors that must be carefully weighed when considering adjuvant therapy options.

“Previously available data were conflicting about how much impact tamoxifen had on invasive vs DCIS recurrences in patients with favourable prognostic factors, so this finding, in such a robust data set, is clarifying,” Wright said.

She pointed out that for patients who choose to forgo radiotherapy, knowing the risk of recurrence with and without tamoxifen can inform 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. Now, we have more data to help our patients choose among these.

“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. I believe that being able to provide clear information to our patients leads to the best care,” Wright said.

The analysis included 878 patients (median age 59 years, 77 percent postmenopausal, 89 percent White), including 317 in NRG/RTOG 9804 and 561 in ECOG-ACRIN E5194. These patients had “good-risk” DCIS, which was characterized as having a disease grade of 1 or 2, disease size of not more than 2.5 cm, and clear surgical margins of at least 3 mm. A total of 378 received adjuvant tamoxifen (43 percent). The median follow-up was 14.85 years.

The study was limited by the lack of information about genomic indicators of prognosis and the inclusion of patients who fit a narrow set of criteria for “good risk.” Wright acknowledged that additional data may be needed to evaluate the findings in patients with different DCIS characteristics.