ESTRO 2024 - Abstract Book

S660

Clinical - Breast

ESTRO 2024

Giuseppe Ronci 6 , Federica Cattani 2 , Paolo Veronesi 4,7 , Roberto Orecchia 8 , Barbara Alicja Jereczek-Fossa 1,7 , Maria Cristina Leonardi 1 1 European Institute of Oncology, Radiotherapy, Milan, Italy. 2 European Institute of Oncology, Unit of Medical Physics, Milan, Italy. 3 European Institute of Oncology, Breast Radiology, Milan, Italy. 4 European Institute of Oncology, Breast Surgery, Milan, Italy. 5 European Institute of Oncology, Experimental Oncology, Milan, Italy. 6 European Institute of Oncology, Pathology, Milan, Italy. 7 University of Milan, Oncology and Hemato-oncology, Milan, Italy. 8 European Institute of Oncology, Scientific Directorate, Milan, Italy

Purpose/Objective:

As of today, the main strategies for early-stage breast cancer treatment include breast-conserving surgery (BCS) and WBRT. Given that the majority of local recurrences occured in close proximity of the tumor bed, APBI, which delivers a larger dosage per fraction to the tumor bed during a shorter treatment duration, is becoming more and more popular as a viable option for selected BC patients. This study aims to report first findings from the CRYSTAL trial, which uses CyberKnife to deliver ablative preoperative RT in a single fraction.

Material/Methods:

CRYSTAL trial (NCT04679454) is a monocentric phase I/II, single-arm and open-label study which enrolls patients to receive an ablative dose (18 –24 Gy) to the tumor with CyberKnife before the surgery. The primary endpoint for the phase I study is the identification of the maximum tolerated dose (MTD) which meets a specific target toxicity level (no grade 3-4 toxicity). For the phase II study, the primary aim is the evaluation of treatment efficacy measured in terms of pathological complete response rate.

Results:

A total of 14 patients with a median age at enrollment of 66.8 years (IQR 63.4 – 69.0) were treated within the study. Nine of them have been enrolled and treated within the phase I of the study (3 patients for each dose step: 18-21 24 Gy) while five were treated within the phase II with 24 Gy in single fraction. Stage at diagnosis was T1N0 for nine patients and T2N0 for 5 patients (luminal A for 10 patients, luminal B for 1 patient, luminal B-HER2+ for 2 patient and triple negative histology for 1 patient). Median PTV volume was 15.1 cm3 (range 3.6-47.8 cm3). At pre-surgery MRI 7 patients experienced stability disease, 4 patients a partial response and one patient a complete response, with a median disease extension reduction of 17.9%. Median time to surgery was 33 days (range 28 – 40 days) with 3 patients who underwent mastectomy and 11 QUAD+BLS. One post-surgical complications (liponecrosis) has been reported. All patients except one experienced a reduction in Ki67 proliferation index (median change between biopsy and histologic exam of 7%). Eleven among the 14 treated patients have received post-operative RT according to study protocol, with two patients receiving also chemotherapy. No G>2 acute toxicities have been reported and only one G1 chronic toxicity (breast pain) has been reported at last follow-up. 1-year follow-up was available for 9 out of 14 patients. At a medium follow up of 13.1 months (range 1.4 – 23.3 months) two patients developed a regional relapse and two patients a second tumor in another site. All the other patients are alive with no evidence of disease.

Figure 1. (a) Overview of the study protocol and (b) example of a preoperative RT treatment plan (24 Gy, 85% isodose).