Abstract:

Checkpoint inhibitor immunotherapy, including pembrolizumab, a programmed cell death-ligand 1 (PD-L1) inhibitor, has been increasingly utilized with favorable outcomes in patients diagnosed with metastatic malignant melanoma. Along with the successful expanded use of this class of medication has been the rise of newly discovered adverse side effects. A 63-year-old woman with a history of choroidal melanoma, treated with radiation therapy two years prior, developed a metastatic lung mass in her right upper lobe. She underwent tumor resection followed by adjuvant pembrolizumab therapy. Shortly after receiving treatment, she noticed two painful subcutaneous nodules on her left hip. A PET scan performed displayed numerous subcutaneous nodules with mild to moderate FDG activity located on the chest, abdominal wall, proximal upper extremities, and lower extremities. The findings were concerning metastatic disease. Excisional biopsy of the left hip lesion revealed a collection of fibroadipose tissue with mixed septal and lobular panniculitis. There was significant subcutaneous necrosis along with a dense inflammatory infiltrate composed of neutrophils, lymphocytes, foamy histiocytes, and scattered eosinophils. Special stains were negative for microorganisms and melanocytic immunohistochemical markers were negative. Taken in conjunction with the development of cutaneous nodules shortly after beginning treatment with pembrolizumab, the histologic findings were most compatible with a cutaneous drug reaction. Following discontinuation of pembrolizumab, the patient showed significant improvement of her lesions. To date, there are few reports of immune checkpoint inhibitors causing panniculitis and subcutaneous fat necrosis, especially with the widespread clinical manifestations seen in this patient. We present this case because it is paramount to recognize these therapy related effects as they can mimic other diseases and can lead to diagnostic and therapeutic implications.

Financial Disclosure:
No current or relevant financial relationships exist.

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Vasudevan Mahalingam, DO, MS