Patterns of loco regional failure in women with breast cancer treated by Postmastectomy Conformal Electron Beam Radiation Therapy (PMERT): Large scale single center experience

Purpose To evaluate loco regional control and describe the patterns of loco regional failure in women with breast cancer irradiated by a previously described post-mastectomy highly conformal electron beam radiotherapy technique. Materials and methods We included all women irradiated by PMERT for non-metastatic breast cancer (BC) between 2007 and 2011 in our department. All cases of bilateral BC were excluded. All patients who experienced loco regional recurrence have been studied. Mapping patterns of regional recurrences was also performed and compared with the ESTRO and RTOG Guidelines of volume definition and delineation guidelines. Results Among the 796 women included, 10.1% were triple-negative (TN) and 18.8% were HER2-positive and 24.6% of them had received neoadjuvant chemotherapy (CT). Internal mammary chain (IMC), supraclavicular (Level IV), infraclavicular (Levels III and II) and axillary LN (Level I) were treated in 85.6%, 88.3%, 77.9% and 14.9% of cases, respectively. With a median follow-up of 64 months (range: 6-102), 5-year locoregional (RFS and OS were 90% (95% CI: 88.1-92.4) and 90.9% (95% CI: 88.9-93), respectively. Twenty-three patients (2.9%) presented locoregional recurrences. Most of them presented aggressive biological features with grade III tumors in 17 patients (74%) with high mitotic index in 16 cases (70%) and triple negative tumors in 12 (52%). Lymphovascular invasion (LVI) was observed in 11 cases (48%). In 14 cases the locoregional recurrences were diagnosed at the same time as the metastatic disease whereas 4 patients presented distant metastases secondarily. Local (Chest wall) recurrences occurred in 13 cases (56%) with the coverage by the isodose of 47.5 Gy (isodose 95%). Fifteen regional recurrences (lymph nodes) were observed in 13 patients. Only 3 regional recurrences occurred within irradiated volumes and 12 regional recurrences occurred outside irradiated areas. Conclusion In presented series, the local recurrences were related mostly to the tumor biological aggressivity and radio resistance. Small number was caused by geographical miss. Further follow-up and careful registration of the recurrences is needed to improve their understanding.