351 - Prospective Evaluation of a Once per Day Regimen of Accelerated Partial Breast Irradiation in Low-Risk, Hormone-Responsive Breast Cancer
Presenter(s)
J. G. Bazan Jr1, N. Ruel2, S. Yoon1, A. L. Schwer3, S. M. Glaser1, S. Szeja4, P. M. Mandelin5, G. Green6, J. H. Kim6, T. Abuali5, and S. Cole2; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2City of Hope Comprehensive Cancer Center, Duarte, CA, 3Department of Radiation Oncology, Orange County Lennar Foundation Cancer Hospital, Irvine, CA, 4City of Hope, Upland, CA, 5City of Hope, Duarte, CA, 6City of Hope, Torrance, CA
Purpose/Objective(s): Previous studies have demonstrated that accelerated partial breast irradiation (APBI) delivered to a dose of 3000 cGy in 5 fractions on consecutive days may have increased rates of late toxicity and decline in patient-reported Global Cosmetic Score (GCS) compared to lower total doses of APBI. We set to evaluate whether APBI delivered to a dose of 2700 cGy in 5 F on consecutive days would result in acceptable patient-reported GCS and toxicities in a single arm prospective protocol.
Materials/Methods: Phase II single arm study including patients =40 years old with stage I (T1N0) hormone-receptor positive/HER2- invasive breast cancer or patients with ductal carcinoma in situ. Initially, patients were required to have physician-reported “Good” (G) or “Excellent” (E) on the Global Cosmetic Score (GCS) to be eligible but protocol was amended after the first patient to require patient-reported E/G cosmesis. All patients received 2700 cGy in 540 cGy daily fractions on consecutive days. Primary endpoint was the rate of acceptable (E/G) cosmesis 1-year post-APBI with a hypothesis that this rate would be =90% and that a 74% rate would be deemed unacceptably low. Based on a one-sided exact test with a=0.05 a sample size of 38 patients would have 82% power to meet these criteria. We estimated that 20% of patients would be lost to follow-up by 1 year, resulting in an accrual goal of 48 patients. Secondary endpoints included physician-rated GCS, blinded physician GCS, physician and patient reported toxicities using CTCAE and PRO-CTCAE, and patient-reported quality of life using the Breast Cancer Treatment Outcome Scale (BCTOS).
Results: 48 patients were enrolled with median age 62 y, 50% with invasive cancer, median ER expression 95%, median PR expression 90%, and 94% with grade 1-2 disease. At 1-year, 39 patients were evaluable. At baseline, 98% (47/48) patients reported E/G GCS and at 1-year, the E/G GCS was 87% (N=34/39; 95% CI 73.3%-94.4%). Physician-reported and blinded investigator-reported E/G GCS at baseline were 97.9% and 87.2% and at 1-year were 100% and 90%. Cosmetic score by the BCTOS improved from 1.40 at baseline to 1.19 at 1-year post-APBI (11.3% relative change, p=0.006). 1 patient experienced acute grade 2 toxicity (fatigue), and there were no late (=6 months) grade =2 toxicities, including breast fibrosis or pain. No patients reported severe or very-severe pain on the PRO-CTCAE, and the incidence of mild/moderate pain decreased from 38% at the end of APBI to 13% at 1-year post-APBI.
Conclusion: Delivery of APBI with 2700 cGy in 5 fractions on consecutive days in patients self-reporting E/G GCS at baseline results in 90% of patients maintaining self-reported E/G GCS. In addition, the GCS by all methods (treating physician and blinded investigators) were =90% 1-year post-radiation. Coupled with the absence of grade 2 late toxicity to date and improvements in the BCTOS cosmetic score, this APBI regimen is safe. Longer term follow-up will continue to assess changes in GCS and cancer control outcomes.