354 - Long-Term Follow-up of a Prospective Multicenter Trial of Endocrine Therapy without Radiotherapy after Breast-Conserving Surgery for Biologically Favorable Stage: Breast Cancers In Younger Postmenopausal Patients
Presenter(s)
R. Jagsi1, K. Griffith2, E. E. R. Harris3, J. L. Wright4, A. Recht5, A. G. Taghian6, B. Jones7, M. S. Moran8, W. Small Jr9, C. Johnstone10, A. S. Rahimi11, G. M. Freedman12, M. Muzaffar13, B. G. Haffty14, K. C. Horst15, S. N. Powell16, J. Sharp17, M. S. Sabel17, A. F. Schott17, and M. El-Tamer18; 1Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA, 2Department of Biostatistics, University of Michigan, Ann Arbor, MI, 3St. Luke's University Health Network, Easton, PA, 4University of North Carolina at Chapel Hill, Chapel Hill, NC, 5Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Boston, MA, 6Harvard Medical School, Boston, MA, 7Northwell, New York City, NY, 8Department of Therapeutic Radiology, Yale School of Medicine, New Haven, CT, 9Department of Radiation Oncology, Stritch School of Medicine, Cardinal Bernardin Cancer Center, Loyola University Chicago, Maywood, IL, 10Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, 11Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 12Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 13East Carolina University, Greenville, NC, 14Rutgers Cancer Institute of New Jersey, Department of Radiation Oncology, New Brunswick, NJ, 15Stanford University School of Medicine, Stanford, CA, 16Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 17University of Michigan, Ann Arbor, MI, 18MSKCC, New York, NY
Purpose/Objective(s): Patients older than age 65-70 years (y) with Stage I ER+ breast cancers are commonly treated with endocrine therapy (ET) without radiotherapy (RT) after breast-conserving surgery (BCS). However, few studies of RT omission included younger patients. We previously reported findings from a prospective single-arm trial for such a population at a median follow-up of 5.2 y. At that time, there were only 2 recurrences before 5 y but 6 more after 5 y, when many patients cease to receive ET. Given concerns about late recurrence in ER+ disease, particularly after de-escalating local-regional therapy, we report updated results.
Materials/Methods: We enrolled 200 postmenopausal patients age 50-69 y at 13 US sites between 2015-2018. Eligibility criteria included having an ER+/PR+/ HER2- pT1N0 unifocal cancer with margins =2 mm and 21-gene recurrence score (RS) =18. Patients agreed to take ET for at least 5 y. The primary endpoint was freedom from breast cancer recurrence 5 y after BCS. Recurrences were categorized as ipsilateral breast events (IBE), regional nodal recurrence, or distant failure. Follow-up (f/u) time was calculated from the date of BCS until first recurrence or to last clinical f/u. The time-to-event endpoint was calculated using the product-limit method of Kaplan and Meier.
Results: The mean age was 62 y (SD 4.9), mean RS 11.2 (SD 4.8), and mean tumor size 10 mm (SD 4.6). Nearly all tumors were Grade 1 or 2 (97%; n=194), with only 3% (n=6) Grade 3. Lymphovascular invasion was present in 8% (n=16) and an extensive intraductal component in 5.5% (n=11). Median f/u time was 7.93 years (95% CI: 7.65-8.05). The 5- and 8-y actuarial rates of freedom from recurrence were 99% (95% CI, 96%-100%) and 94% (95% CI, 89%-97%). Ten patients (5%) developed IBEs from 49-102 months after BCS, of which 9 occurred after 5 y; 7 of these were treated with repeat BCS and 3 with mastectomy. Crude IBE rates for the entire follow-up period were 5% (3/60) for patients aged 50-59 and 5% (7/140) for patients aged 60-69; crude rates of overall relapse were 7% (4/60) and 5% (7/140), respectively. One patient developed a regional-only recurrence 21 months after BCS and was treated with axillary dissection and nodal RT. No distant recurrences were observed.
Conclusion: Our trial showed that ET without RT resulted in a low risk of cancer relapse at nearly 8 y median f/u for this highly selected group of younger postmenopausal women. Only 3 of the 200 patients underwent mastectomy. The great majority of IBE occurred more than 5 y after BCS, emphasizing the importance of long-term surveillance. Synthesis of our long-term results with those from other prospective studies and ongoing randomized trials is essential to inform patient decisions, particularly in an era when RT can be delivered with limited toxicity in as little as 1 week.