Abstract PS2-05-07: Evaluation of fusion imaging guidance in radiofrequency ablation for early-stage breast cancer

Abstract Background: Radiofrequency ablation (RFA) for early-stage breast cancer with tumors ≤15 mm in diameter was approved for coverage under Japan’s national health insurance in December 2023, following favorable results from several clinical trials. Clinical RFA procedures commenced at our institution in May 2024. Small early-stage breast cancers—especially non-mass lesions—are often difficult to visualize or delineate using conventional B-mode ultrasound (US) alone. Additionally, gas formation during RFA may obscure the lesion, complicating precise localization for additional ablation. This study aimed to evaluate the clinical utility of fusion imaging combining contrast-enhanced breast magnetic resonance imaging (MRI) with US and/or contrast-enhanced US (CEUS) to improve lesion targeting and procedural accuracy during RFA. Patients and Methods: Fourteen patients with early-stage breast cancer underwent RFA guided by fusion imaging. A volume navigation system (LOGIQ E10x, GE Healthcare) was used to fuse dynamic contrast-enhanced MRI with US, aligning anatomical landmarks such as the nipple to ensure accurate lesion localization. CEUS using Sonazoid® was performed to evaluate intratumoral microvascularity. A Cool-tip needle (Medtronic, CO, USA) was inserted with a planned 1-cm safety margin around the tumor. Intratumoral impedance was measured upon insertion, and 10-20 mL of 5% glucose was injected into the retromammary space to prevent heat diffusion. Ablation was initiated at 5 W and continued until automatic roll-off occurred, due to increasing impedance. Therapeutic efficacy was assessed ≥4 weeks post-procedure using follow-up imaging and ultrasound-guided vacuum-assisted biopsy (US-VAB) of the ablation zone. Results: Patient ages ranged from 34 to 82 years (mean: 57 years), with tumor sizes from 7 to 15 mm (mean: 12.4 mm). Histopathologic findings included ductal carcinoma in situ (DCIS; n=8) and invasive ductal carcinoma (IDC; n=6). Molecular subtypes included Luminal A-like (n=4) and Luminal B-like (n=2). Tumors were located in the upper outer quadrant (n=8), upper inner quadrant (n=2), lower outer quadrant (n=2), and deep medial or axillary tail regions (n=1 each). Fusion imaging significantly improved visualization and delineation of lesions that were challenging to identify with B-mode US alone. It also enabled accurate re-localization of the original lesion during additional ablation sessions, resulting in successful complete ablation in all cases. Initial impedance ranged from 116 to 245 Ω (mean: 169 Ω), maximum ablation temperature from 83°C to 100°C (mean: 93°C), and ablation time from 14 to 32 minutes (mean: 20 minutes). One case of postoperative nipple retraction was observed; no other major complications occurred. No viable cancer cells were detected in any US-VAB specimens. Conclusion: Fusion imaging combining contrast-enhanced MRI with US/CEUS enhances the precision, safety, and efficacy of RFA for early-stage breast cancer, particularly for lesions that are poorly visualized on conventional US. Further accumulation of clinical cases is needed to standardize fusion imaging protocols and optimize outcomes. Citation Format: C. YAMANAKA, S. MATSUZAKI, Y. HAYAKAWA, H. MANABE, M. KUBOTA, T. ITO, Y. KOMOIKE. Evaluation of fusion imaging guidance in radiofrequency ablation for early-stage breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-05-07.