Sep 28

SS 07 - Breast Cancer 1: Redefining Radiation Schedules: Hypofractionation and APBI Across the Breast Cancer Spectrum

143 - Accelerated Partial Breast Irradiation to 40 Gy in 10 Daily Fractions: Long-Term Results of a Phase II Study

05:15pm - 05:25pm PT

Room 301-304

Presenter(s)

Kaitlyn Lapen, MD - Memorial Sloan Kettering Cancer Center, New York, NY

K. Lapen¹, L. A. Boe², B. A. Mueller³, D. A. Roth O’Brien³, J. J. Cuaron³, M. B. Bernstein¹, A. J. Xu³, I. J. Choi³, B. McCormick³, A. J. Khan³, S. N. Powell³, and L. Z. Braunstein³; ¹Memorial Sloan Kettering Cancer Center, New York, NY, ²Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, NY, ³Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s):

Several approaches to accelerated partial breast irradiation (APBI) demonstrate comparable tumor control, yet patient-reported outcomes (PRO) and cosmesis vary. Concerns regarding optimal dosing and fractionation persist. Herein, we report the 10-year results of a prospective phase II study evaluating APBI to 40 Gy in 10 daily fractions.

Materials/Methods:

Patients were enrolled on a single-arm phase II study to receive APBI to 40 Gy in 10 daily fractions following breast conserving surgery (BCS) for early-stage invasive or in situ breast cancer. Patients had to have pathologically node-negative disease. APBI was delivered using 3D-conformal radiotherapy and the planning target volume (PTV) was limited to <35% of the ipsilateral whole-breast volume. Patient and clinician-reported outcomes were collected for salient adverse effects annually following APBI.

Results:

Between 2010 and 2014, 106 patients enrolled and received APBI; median age was 62 years (range 39-85 years) and median follow-up at this final report is 11 years (range 3-14 years).

Clinician-reported outcomes revealed grade 2 cutaneous toxicities in 8% (n = 8) of patients, grade 2 late skin toxicity in 3% (n = 3), and grade 2 breast edema in 1% (n=1). A single instance of grade 3 late skin toxicity arose in 1 patient (1%) 5 years after APBI, consisting of extensive telangiectasias.

PRO showed that 21% (n=21) and 2% (n=2) of patients reported maximum pain at the site of APBI as grade 2 and 3, respectively, at a median time of 13 months (IQR 7-37 months) after APBI. At last follow-up, 4% (n=4) of patients reported grade 2 pain. Overall, 7% (n=7) of patients self-reported grade 2 skin toxicity and 2% (n=2) reported grade 3 (2 cases of cellulitis). 8% (n=8) of patients reported grade 2 breast swelling while 2% (n=2) reported grade 3 breast swelling. At last follow-up, 47% (n=46) of patients self-reported excellent cosmesis, 48% (n=47) reported good cosmesis, and 5% (n=5) reported fair cosmesis; no patients reported poor cosmesis.

Three local recurrences (LR) were observed: one at 3 years following diagnosis and two at 5 years, yielding a 10-year cumulative incidence of LR of 3% (95% CI 0.8-8%). A single distant recurrence (DR) arose in the study cohort 2 years following diagnosis, for a 10-year cumulative incidence of DR of 1% (95% CI 0.1-5%). 3 (3%) patients were diagnosed with a contralateral breast cancer during the follow-up period, all more than a decade after initial diagnosis (at 10, 11, and 13 years).

Conclusion:

At a median follow-up of 11 years, APBI delivered to 40 Gy yields excellent disease control among appropriately-selected patients (10-year LR of 3%). This regimen shows excellent tolerability following BCS, with 95% of patients reporting excellent or good cosmesis at final follow-up. As clinical adoption continues to expand, this study further supports the efficacy of APBI and presents a viable fractionation schedule.