Metastatic Signet-Ring Melanoma Masquerading as Obstructive Pneumonia

    A 50-year-old white man presented with a five-month history of progressively worsening purulent cough.  Past history was significant for nodular melanoma with spindle cell features of the left mastoid, Breslow depth 3.2 mm, diagnosed eight years prior.  The tumor was treated with wide local excision and sentinel lymph node biopsy and computed tomography were negative. The patient did well for five years until he presented with a small-bowel obstruction due to metastasis.  He underwent small-bowel resection.  Imaging revealed a lung mass in the left lower lobe.  Biopsy was consistent with melanoma and he was started on combination chemotherapy with temozolomide and a poly-adenosine diphosphate-ribose polymerase inhibitor.  The tumor grew, chemotherapy was discontinued, and a multipeptide vaccine plus denileukin diftitox were initiated.  He subsequently developed fever, productive cough and a new lung opacity on chest radiography. Following inadequate response to antimicrobial therapy, biopsy was performed during bronchoscopy, which revealed a mass occluding 90% of his left lower lobe.  The patient was treated with thoracotomy with left lower lobe resection.

    Histopathology revealed a pleomorphic, highly atypical spindled proliferation with a surrounding mixed lymphoplasmacytic inflammatory infiltrate.  Immunohistochemistry for MITF, TTF1, and cytokeratin AE1/AE3 were negative. Sections labeled for S-100 were diffusely positive.