Top Line: A combined look at trials assessing radiation omission for good-risk ductal carcinoma in situ (DCIS) sharpens the radiation versus tamoxifen monotherapy discussion.
The Study: This pooled ancillary analysis of the radiation omission arms of RTOG 9804 and ECOG-ACRIN E5194 yields 878 patients with “good risk” DCIS s/p breast-conserving surgery. To review, low-risk here is mammographically detected, low/intermediate grade, tumors ≤2.5 cm, margins ≥3 mm. What makes for novel data here is that roughly 43% of these women received tamoxifen at physicians/patient discretion affording us a first look at how endocrine therapy alone influences recurrences risk specifically for good-risk DCIS. Receipt of tamoxifen use reduced 15-year ipsilateral breast recurrence at 15 years from 19% to 11% (HR 0.52), driven by decreases in invasive recurrence from 12% to 6% (HR 0.47). This is remarkably similar to that achieved with radiation where ipsilateral breast recurrences are reduced from 15% to 7% (HR 0.36) and invasive recurrence from 10% to 5%. What has most notably diverged over time are the therapies. Tamoxifen remains a years-long regimen of poorly-tolerated hormone deprivation while radiation for good-risk DCIS now entails 5 highly-conformal 10-minute treatments that most commonly confer no notable side effects.
TBL: For good-risk DCIS, the decision for radiation versus endocrine monotherapy hinges more on a distinction in side effects versus anticipated benefits. | Wright, Int J Radiat Oncol Biol Phys 2026
The Study: This pooled ancillary analysis of the radiation omission arms of RTOG 9804 and ECOG-ACRIN E5194 yields 878 patients with “good risk” DCIS s/p breast-conserving surgery. To review, low-risk here is mammographically detected, low/intermediate grade, tumors ≤2.5 cm, margins ≥3 mm. What makes for novel data here is that roughly 43% of these women received tamoxifen at physicians/patient discretion affording us a first look at how endocrine therapy alone influences recurrences risk specifically for good-risk DCIS. Receipt of tamoxifen use reduced 15-year ipsilateral breast recurrence at 15 years from 19% to 11% (HR 0.52), driven by decreases in invasive recurrence from 12% to 6% (HR 0.47). This is remarkably similar to that achieved with radiation where ipsilateral breast recurrences are reduced from 15% to 7% (HR 0.36) and invasive recurrence from 10% to 5%. What has most notably diverged over time are the therapies. Tamoxifen remains a years-long regimen of poorly-tolerated hormone deprivation while radiation for good-risk DCIS now entails 5 highly-conformal 10-minute treatments that most commonly confer no notable side effects.
TBL: For good-risk DCIS, the decision for radiation versus endocrine monotherapy hinges more on a distinction in side effects versus anticipated benefits. | Wright, Int J Radiat Oncol Biol Phys 2026