Select patients with early-stage breast cancer who achieved exceptional responses to ablative radiation therapy and endocrine therapy were able to omit surgery without disease progression, according to findings from a prospective phase II trial presented during the Congress of the European Society for Radiotherapy and Oncology (ESTRO 2026; Abstract 4177).
“Historically, treatment de‑escalation in breast cancer has focused on reducing hormone therapy duration or the amount of radiation,” said presenting author Simona Shaitelman, MD, Professor of Breast Radiation Oncology at The University of Texas MD Anderson Cancer Center. “What’s exciting now is that advances in radiation delivery are opening the door to entirely new nonoperative approaches that many patients have been asking about.”
Study Methods
The phase II trial enrolled 20 eligible patients with hormone receptor–positive, HER2-negative, stage I nonlobular breast cancer who had an Oncotype DX score of 25 or below and were aged 50 years or older. These patients were treated with 3 months of endocrine therapy and were then restaged and underwent definitive ablative radiotherapy (37.5 Gy in five fractions every other day), with the use of a magnetic resonance (MR) linear accelerator when possible.
About 6 to 12 months after radiotherapy, the patients underwent percutaneous vacuum-assisted, image-guided core biopsy (VAIGCB) to determine if surgery was recommended or not. If the patient had a pathological complete response, they were able to omit surgery.
Key Findings
Eighty percent of patients were able to be treated with the MR linear accelerator, and the remained received a linac with computed tomography on rails; 95% underwent VAIGCB, as one patient declined.
Of the 19 patients biopsied, 10 (53%) achieved a pathologic complete response (95% confidence interval [CI] = 30%–73%). The pathologic complete response rate for biopsies performed within 6 months of radiation was 45% (95% CI = 19%–72%) and 63% (95% CI = 27%–87%) for biopsies done within 12 months.
The baseline volume of tumor as assessed by ultrasound did not correlate with the VAIGCB pathologic complete response status (P = .29), but there was a correlation for both the volume at 3 months after endocrine therapy (P = .02) and the percent volume decrease from baseline (P = .04) with pathologic complete response status.
The median follow-up was 37.3 months for patients who could omit surgery; at that point, the disease progression rate was 0%.
The 3-year progression-free survival rate was 92% (95% CI = 54%–99%). One patient died from non–breast cancer–related causes.
“Radiation therapy is widely accessible around the world, yet its full potential as a definitive treatment for breast cancer hasn’t been fully explored,” Dr. Shaitelman said. “With more than two million women diagnosed each year, patients have varied goals and preferences, and it’s critical that we rigorously study nonsurgical options to see whether they can deliver outcomes comparable to standard breast surgery.”
DISCLOSURES: For full disclosures of the study authors, visit estro.org.
