Figure 2.

A photomicrograph at ×20 magnification, showing an endobronchial papilloma comprising complex papillary fronds with fibrovascular cores lined by columnar mucinous epithelium, with high-grade cytological atypia. The papilloma was negative for thyroid transcription factor-1 (TTF-1) and Napsin A. Some basal cells were highlight by p63, and Ki-67 proliferation was around 5%.