Long-Term Results of Post Mastectomy Conformal Electron Therapy Technique (PMERT) with Bolus in Comparison with Post Mastectomy Conformal Photon Therapy (PMPhRT) without Bolus in Non-Metastatic Breast Cancer Patients

Abstract

To evaluate locoregional control, survival and toxicity after mastectomy, in patients irradiated by a postmastectomy highly conformal PMERT using bolus in comparison with highly conformal PMPhRT without bolus in the adjuvant setting of breast cancer (BC) patients. We included women irradiated by postmastectomy radiation therapy for non metastatic BC before 2012 in 2 of our institute sites using respectively one of the 2 studied techniques. All patients have been treated to total dose of 50 Gy in 25 fractions. Toxicities were assessed using CTCAE v.4.0. Qualitative data were described as proportions and compared using Chi-2 or Fischer’s exact test. Locoregional recurrence free survival (LRFS), locoregional recurrence free interval (LRFI), overall survival (OS) and metastasis free interval (MFI), defined as the time between the end of treatment and the 1st event of interest among recurrence (LRFI and LRFS), metastasis (MFI), death (LRFS and OS), were estimated using Kaplan-Method method and compared with a log-rank test. Patients without any event were censored at their date of last news. Among the 1097 patients, 796 have been treated by PMERT (387 left, 409 right) and 301 by PMPhRT (162 left, 139 right). The median follow up was 64 and 63 months for PMERT and PMPhRT, respectively. In the PMERT group, median age was 52 yrs (22-91), 10.1% were triple-negative (TN), 18.8% HER2-positive, 24.6% received neoadjuvant chemotherapy (CT) and 51.3% had multifocal lesions. In the PMPhRT group, median age was 55 yrs (28-89), 10 % were TN, 15.3% HER2-positive, 22.2% received CT and 48.8% had multifocal lesions. At least 1 involved lymph node (LN) was observed in 64.6% and 74.4% (p=0.002) for PMERT and PMPhRT respectively. Internal mammary chain, supraclavicular, infraclavicular, and axillary LNs were treated in 85.6%, 88.3%, 77.9%, and 14.9% of cases, respectively for PMERT and for the PMPhRT group: 75.4% (p < 0.05), 84.7% (p = 0.11), 83.4 % (p < 0.05) and 19.6% (p = 0.06). Five year LRFS and OS were 90% (CI95%[88.1;92.4]) and 90.9% (IC95%[88.9;93]), respectively for PMERT and 86.3% (CI95%[82.4-90.4]) and 89.2% (CI95%[85.6-93]), respectively for PMPhRT. There were no significant difference in OS (p=0.68), LRFS (p=0.08) and MFI (p=0.16) between the 2 groups. PMPhRT was significantly associated wih a higher risk of locoregional relapse (HR=2.63 [1.4 ; 4.94], p=0.003). Early skin toxicity was scored as grade 1 in 58.5% vs 78.7%, grade 2 in 35.9% vs 11.3%, and grade 3 in 4.5% vs 1.3% of patients, respectively for PMERT and PMPhRT, (p<0.05). At long-term follow-up, 29.8% vs 14.3% of patients presented temporary or permanent pigmentation or telangiectasia or fibrosis for PMERT and PMPhRT respectively. Higher risk of local recurrences was observed in the group of PMPhRT without bolus in comparison with the group of PMERT using bolus. Dosimetric study is needed to evaluate the skin dose in patients treated without bolus by photons, as well as a detailed description of the recurrences