Non-neoplastic inflammatory pseudotumor of the lung after immunotherapy for melanoma: A diagnostic pitfall on fine needle aspiration biopsy of lung.

Nivolumab is commonly used as monotherapy or in combination therapy for management of locally advanced or metastatic melanoma; however, it is also associated with immunotherapy-related adverse events concerning for disease progression or tumor flare reaction. This report presents a case of a non-neoplastic pseudotumor of the lung initially mistaken for malignancy that occurred in a patient receiving adjuvant nivolumab therapy following complete resection of stage IIIB melanoma. The diagnosis was made by lung biopsy and confirmed by a wedge resection, with findings consistent with organizing pneumonia type of pulmonary inflammatory pseudotumor rather than malignancy.