ESTRO 2024 - Abstract Book

S622

Clinical - Breast

ESTRO 2024

Purpose/Objective:

The phase III randomized clinical DBCG Skagen trial 1 (NCT02384733) randomized 2946 node-positive breast cancer patients from seven countries to 50Gy/25fr versus 40Gy/15fr for loco-regional radiotherapy (RT) during 2015-2021. The primary endpoint was 3-yr ipsilateral arm lymphedema. As part of the trial, all target volume delineation had to follow the ESTRO consensus guideline for target volume delineation in early breast cancer[1]. Patients could have locally advanced breast cancer and receive neoadjuvant systemic therapy before surgery (mastectomy/lumpectomy), or they had surgery soon after diagnosis followed by adjuvant systemic therapy and were followed regarding morbidity and failures. Nodal boost was not allowed in the trial, thus no patients had macroscopic visible nodal disease at the time of RT. The RT planning was mostly based on tangential fields and 3D conformal technique. Report of loco-regional pattern of failure according to ESTRO guideline was pre-specified in the trial protocol with the objective of validating the clinical feasibility of the ESTRO guideline in high-risk breast cancer patients.

Here we present the first analysis of the pattern of failure in patients from the DBCG Skagen trial 1.

Material/Methods:

Loco-regional failure with or without distant failure as the first event was defined from all available imaging. Local failure was present if there was DCIS or invasive carcinoma detected inside the mammary region (skin, scar, subcutaneous tissue, breast or chest wall muscle), and regional failure was reported for failures in the ipsilateral nodal volumes defined in the ESTRO consensus. The failures were classified as inside the high-dose volume, at the edge of the high-dose volume (close to the CTV and high-dose volume but not covered with high-dose), or outside. High-dose volume in the mammary region was defined by the 95% isodose and the high-dose volume for the nodal volume by the 90% isodose as per DBCG guideline[2]. The proximity of a failure to the CTV was also investigated. At time of analysis complete imaging information was only available in the 2080 patients from Denmark, thus this study reports the failure pattern in this sub-group. The information about localization of the failures was matched with the diagnostic imaging and the planning CT scan to report if the failures were at the same site as the primary tumor and/or if nodal metastases could be detected in retrospect.

Results:

The seven Danish centers recruited 2080 patients. At a median follow-up of 4.5 years, locoregional recurrence was present in 60 patients; 29 patients with isolated locoregional failure and 31 with locoregional failure concurrent with distant failure. All patients except one had the loco-regional failure in the high-dose volume (table 1). For the 29 patients with isolated loco-regional failure, all failures were in the high-dose volume; one had failure inside the high-dose volume but outside the CTV. For the 31 patients with loco-regional failure with concurrent distant failure, one had nodal failure at the edge of the high-dose volume (figure 1) and two had failure inside the high-dose volume but outside the CTV.