Long-term outcome from RTOG 9517: A phase I/II study of accelerated partial breast irradiation (APBI) with mulitcatheter brachytherapy (MCT) following lumpectomy for early-stage breast cancer.

Abstract

147 Background: Comparison of APBI to whole breast irradiation post lumpectomy for breast conservation is ongoing in phase III trials. However, APBI has gained acceptance in clinical practice despite relatively limited long-term data. RTOG 9517 studied MCT, one of the earliest methods of APBI, and can uniquely provide long-term cancer outcomes. Methods: Eligibility was stage I/II unifocal breast cancer <3cm, invasive non-lobular histology without EIC, negative surgical margins, and 0-3 positive axillary nodes; no extracapsular extension. The target volume was the lumpectomy cavity plus a 2 cm radial and 1 cm ant/post margin. Low Dose Rate (LDR), 45 Gy in 3.5-5 day, or High Dose Rate (HDR) 34 Gy in 10 BID fractions over 5 days was delivered. A rapid dosimetry review was done to assure dose delivery per protocol. Systemic therapy was per physician’s discretion. The primary endpoint was HDR and LDR MCT reproducibility. This analysis focuses on ipsilateral breast failure (IBF), contralateral breast cancer events (CBE), regional (RF) and distant failure (DF) (cumulative incidence) disease-free (DFS), relapse-free (RFS), and overall survival (OS), (Kaplan-Meier). Results: The median follow up is 12.1 years (yr). 100 patients were accrued from 1997-2000; 98 were evaluable; 65 HDR and 33 LDR MCT. Median age was 62; 88% had T1 tumors; 12% T2; 81% p N0, 19% pN1; 77% ER and/or PR +; 19% ER - and PR -; 33 % received adjuvant chemotherapy and 64% antiendocrine therapy. There have been 6 IBF for a 10 yr rate of 6.2%; 2 IBF were outside the APBI field. There were 5 total RF for a 10 yr rate of 5.2%, respectively. There have been 5 CBE for a 10 yr rate of 4.2%. Failure patterns were: 4 isolated IBF, 1 isolated RF, 8 DF only, 1 IBF+RF, 1 IBF+RF+DF, 1 RF+CBE, 1 RF+DF, 3 CBE, and 1 CBE+DF (21 total failures). Eleven patients have developed DF; 8 have died of breast cancer, 22 have died from other causes. The 10 yr DFS, RFS and OS are 69.8%, 71.9%, and 78.0%, respectively. Conclusions: This multi-institutional phase II trial studying MCT-APBI continues to report durable local regional cancer control rates with long term follow-up. Supported by NCI U10 grants CA21661 and CA37422.