Exceptional Pathological Complete Response Following Concurrent Neoadjuvant Pembrolizumab and Radiotherapy for Locally Advanced Cutaneous Angiosarcoma: A Multidisciplinary Case Report and Literature Review

Abstract

Cutaneous angiosarcoma is a rare, highly aggressive malignant vascular neoplasm characterized by high rates of local recurrence and distant metastasis despite multimodal therapy. Surgical resection with negative margins remains the cornerstone of curative management. However, achieving complete resection is often challenging in patients with locally advanced disease. Emerging evidence suggests that immune checkpoint inhibitors may provide clinical benefit in selected patients, particularly when combined with radiotherapy, although prospective data remain limited. Here, we report a case of a 53-year-old man who presented with a rapidly enlarging erythematous mass over the posterior aspect of the left shoulder. Histopathological examination confirmed angiosarcoma. Magnetic resonance imaging (MRI) demonstrated a large, hypervascular superficial soft tissue tumor with prominent vascular channels, while staging positron emission tomography/computed tomography showed localized disease without distant metastases. Following a multidisciplinary tumor board discussion, the patient received neoadjuvant radiotherapy (50 Gy in 25 fractions using volumetric modulated arc therapy with daily image guidance) administered concurrently with pembrolizumab. The treatment regimen was well tolerated. An interval MRI revealed a prominent radiologic response, showing significantly reduced tumor enhancement, resolved satellite lesions, and a loss of both diffusion restriction and mass-like architecture. The patient subsequently underwent preoperative tumor embolization followed by radical surgical resection with staged reconstruction. Final pathological examination demonstrated a complete pathological response (ypT0) with negative surgical margins and no residual viable angiosarcoma. Molecular profiling did not identify actionable genomic alterations or biomarkers predictive of an exceptional immunotherapy response. Following a repeat multidisciplinary discussion, pembrolizumab was continued in the perioperative setting to complete 1 year of treatment. This case demonstrates an exceptional complete pathological response following neoadjuvant pembrolizumab administered concurrently with radiotherapy for locally advanced cutaneous angiosarcoma. Given the absence of established predictive molecular biomarkers, this report adds to the growing evidence supporting immunotherapy-based multimodal treatment strategies and highlights the importance of multidisciplinary decision-making in the management of this rare malignancy.