Abstract P1-10-01: Postmastectomy electron beams radiation therapy (PMERT) : long term results
Authors: Sami Souidi , Loap Pierre , Fourquet Alain , Kirova Youlia M. 
Published: March 2023

Background/Purpose: This study evaluates the toxicity after radiotherapy after mastectomy without reconstruction in patients irradiated to the chest wall using previously reported technique of PMERT.

Materials/Methods: We included all women irradiated after mastectomy for not metastatic breast cancer with PMERT between 2007 and 2011 in the Department of Radiation Oncology of the Institut Curie. Previously reported technique using mostly electrons was evaluated in terms of efficacy and toxicity. Acute and late toxicities were assessed retrospectively using CTCAE v.4.0. A clinical exam was weekly performed during radiotherapy and one and three months following the completion of radiotherapy. Patients were then followed as recommended in Institut Curie guidelines (Senorif). Quantitative and qualitative data were described respectively as means and proportions. Statistical comparisons were computed using X² or Fischer’s exact test for categorical data. Recurrence free survival (RFS) was defined as the time between the end of treatment and the date of recurrence or death. Overall survival was the same but recurrences were not taken into account. Patients who did not experienced any event were censored at the date of last news.

Results: Among the 796 women included, 51.3% had multifocal lesions, 10.1% a triple negative (TN) status and 18.8% a HER2+ positive status; 196 (24.6%) received a neoadjuvant chemotherapy, and 208 (26.1 %) a systemic therapy during radiotherapy (chemotherapy and/or targeted therapy); 514 (64.6%) had at least one positive lymph node (LN). Internal mammary chain (IMC) was treated in 85.6% of cases, supraclavicular LN (L4) in 88.3% of cases, infraclavicular (L3-2-IP+/- L1) LN in 77.9% of cases and low axilla (L1) in 14.9% of cases. With a median follow up of 113 months [range : 2-164] locoregional recurrence-free survival and overall survival at 10 years were respectively 94.02 (IC95% : 92.13-98.94) and 79.84 (IC95% : 76.83-82.97). The median survival was not reached. In the long term, 29.6% of patients had telangiectasia (grade 1: 23.3%, grade 2: 5.2% Grade 3: 1.1%). Totally 279 patients (35.1%) had breast reconstruction, on average 21 months after the end of radiotherapy. Twenty-five patients (3%) had early esophageal toxicity, not exceeding the grade 1. Of these patients, 21 had had chemotherapy and all were irradiated on the lymph nodes (24 including the IMC). Irradiation of the IMC was not associated with an increased chronic lung toxicity (OR=1.03 [0.98-1.09]). There were 35 patients who developed heart disease after the end of the treatment. Of them, 30 patients had received anthracyclines (p=1.05) and 9 trastuzumab (p =1.09). Four patients developed ischemic heart disease, 3/4 irradiated on the left chest wall, all on the CMI and supra and infraclavicular LN, but all of them presented multiple cardiovascular risk factors (2 to 4).

Conclusions: Our series have shown that the PMERT using the Institut Curie technique is effective and well tolerated.

Table 1. patients and tumor characteristics (n=796). HR+ : hormonal receptor positive HER2+ : HER-2 overexpressed Cardiovascular risk factor : (smoking, hypertension, dyslipidemia, diabetes, obesity, family history of coronary heart disease or vascular events) as described by the French Health Authority (HAS, Haute Autorité de Santé).

Table 2. Efficiency (n=796, median follow-up: 113 months; range : [2-164]). HR+ : hormonal receptor positive HER 2+ : Her-2 overexpressed TNBC : Triple negative or basal-like cancer, OS : overall survival LRFS : local recurrence free survival LRRFS : locoregional recurrence free survival MFS : metastasis free survival

Multivariate analysis : long term toxicity IMC irradiation : Irradiation of the internal mammary chain, OR : Odd ratio

Citation Format: Souidi Sami, Pierre Loap, Alain Fourquet, Youlia M. Kirova. Postmastectomy electron beams radiation therapy (PMERT) : long term results [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-01.