Nivolumab induced pulmonary sarcoid-like granulomas with a concurrent pleural schwannoma: A pathologic-radiologic correlation of a rare condition mimicking metastatic melanoma.

Nivolumab is an anti-PD-1 antibody. The mechanism of action of nivolumab is inhibition of binding between PD-1 and PD-1 ligand. This causes activation of antigen-specific T cells that were previously unresponsive to cancer cells. This unique mechanism of action attributes the widespread use of nivolumab for the treatment of a variety of neoplastic conditions. On the other hand, this mode of action is associated with adverse effects as well. Schwannoma, also called neurilemmoma, is a benign peripheral nerve sheath tumor. Pleural schwannomas are very rare and very few cases have been reported in the medical English literature so far. Herein, we report a very rare case of concurrent presence of Nivolumab induced pulmonary sarcoid-like granulomas along with primary benign pleural schwannoma in a 49-year-old male. He was diagnosed with malignant melanoma of the right upper arm for which he underwent surgery and was receiving adjuvant chemotherapy. He developed pneumonitis during chemotherapy, and on imaging multiple reticular and nodular interstitial infiltrates were seen along with an incidental pleural mass with a high suspicion for metastasis. Wedge biopsy of the interstitial infiltrates was done and they were found to be pulmonary granulomas related to the nivolumab therapy he was receiving. The patient underwent excision of the pleural mass which showed histopathological and immunohistochemical features of schwannoma. The two conditions are unrelated and rarely encountered simultaneously. The radiologic and pathologic correlation along with differential diagnosis of these conditions are discussed.

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