Pleomorphic (spindle and squamous cell) carcinoma arising in a peripheral mixed squamous and glandular papilloma in a 70-year-old man.

Solitary papillomas of the bronchial tree are rare, particularly in the distal airways. When encountered, solitary papillomas are not frequently found to undergo malignant transformation. When this does happen, it is usually a squamous cell carcinoma arising in a human papillomavirus-associated squamous papilloma (usually in a central airway). Here we report a unique case of pleomorphic (spindle and squamous cell) carcinoma arising in a mixed glandular and squamous papilloma without human papillomavirus association.