Pembrolizumab-induced Sarcoid-like Reactions during Treatment of Metastatic Melanoma

Pembrolizumab is a programmed cell death protein 1, or PD-1, inhibitor therapy immunotherapy for patients with advanced melanoma. This report discusses a series of documented cases of sarcoid-like reactions associated with this therapy. Three patients with malignant melanoma developed metastatic disease and were treated with pembrolizumab immunotherapy. Subsequent imaging showed lymphadenopathy in the mediastinum and hilar regions that was confirmed to represent a sarcoid-like reaction at histologic examination. Radiologists should be aware of the association between pembrolizumab and the development of sarcoid-like reactions to avoid inaccurately ascribing these imaging findings to metastatic disease. Clinical presentation, biopsy, radiographic evidence of bilateral hilar lymphadenopathy (with paratracheal lymphadenopathy), and elevated serum angiotensin-converting enzyme levels aid in the diagnosis of sarcoid-like reactions and help avoid these reactions being mistaken for recurrent or metastatic disease.