Durable Response to Cemiplimab in Advanced Cutaneous Squamous Cell Carcinoma With Extensive Gluteal and Sacral Bone Infiltration: A 12-Month Case.

Cutaneous squamous cell carcinoma (cSCC) is a common skin malignancy, which, in its advanced stages, may involve regional lymph nodes and osseous structures, resulting in poor prognosis. Massive tumor infiltration of the sacrum and pelvic bones is rare and typically associated with limited treatment options and unfavorable outcomes. We present the case of a 59-year-old male with advanced cSCC involving the gluteal region, sacrum, pelvic lymph nodes, and bones. As part of a personalized treatment approach, the patient received a combination of cemiplimab, a PD-1 checkpoint inhibitor, and denosumab for bone protection. Despite the aggressive nature and anatomical complexity of the disease, the patient demonstrated a marked and durable clinical response, with radiographic evidence of partial metabolic regression on PET/CT (SUVmax reduction from 9.87 to 6.37), resolution of sacral pain, and full recovery of ambulatory function. No serious immune-related toxicities were observed. This case illustrates the potential of integrating immunotherapy with supportive bone-targeted therapy to achieve meaningful disease control in rare presentations of bone-invasive cSCC.