Session Item

Breast-conserving surgery (BCS) followed by postoperative radiation therapy (RT) to the residual breast represents the current standard of care for most women affected by early breast cancer (BC). However, standard postoperative regimens are characterized by postsurgical waiting time, socioeconomic consequences and potential acute and late locoregional adverse events. Several studies suggested that BC cells can be more sensitive to high doses administered in short intervals. Preoperative robotic stereotactic radiosurgery (prRS) followed by BCS may yield potential advantages in selected patients. An exploratory phase II study (ROCK trial – NCT03520894) was conducted in our institution.

Women with histologically proven unifocal invasive hormonal receptors positive, HER2 negative BC, sized less than 25 mm, with negative clinical nodal status, aged 50+ and eligible for BCS were enrolled. Fiducial markers were introduced in peri/intralesional position. Magnetic resonance imaging (MRI) was used in addition to standard CT-based planning. Patients received 21 Gy in single fraction with CyberKnife^® followed by BCS two weeks after prRS. The primary endpoint was the acute skin toxic effect rate. Secondary objectives were the pathological response rate and late adverse events. Echocardiography and spirometry were performed before prRs and yearly thereafter. Translational research was conducted to identify correlations between radiogenomic, immunological and biochemical biomarkers with treatment-related response and toxicity.

From August 2018 to September 2021, a total of 70 patients were screened on mammography; 29 of them were eligible following inclusion criteria. Of those, seven were excluded due to multiple foci disease at basal MRI, and 22 patients were successfully treated. All required dosimetric parameters were met in all patients, as well as normal tissue constraints. Median age at diagnosis was 68 years (range 50-86) and median tumor size was 13 mm (range 7.5-25). All treated patients received surgery within 14 days from prRS without any delay or complication. No patients experienced acute skin toxicity of grade (G) 2 or higher, only one patient had a G1 erythema one month after BCS. According to Chevallier’s classification, two patients had a pathological complete response (pCR). At a median follow up of 18 months, no patients experienced locoregional recurrence or distant metastases. No clinically meaningful changes were observed regarding left-ventricular ejection fraction, FEV1 or DLCO.

At a median follow up of 18 months, the ROCK trial showed that single dose prRS is a feasible technique in selected BC patients with a good safety profile and encouraging activity. This new approach in BC management warrants further investigations.