Fig. 2
p16INK4a immunohistochemistry in various cases. a: Inverted papilloma with positive p16INK4a reaction. The case had HPV-16 infection with episomal form. Bar = 200 μm. b: Inverted papilloma with positive p16INK4a expression. Human papillomavirus genome was not identified in this case. Bar = 200 μm. c: Inverted papilloma with positive p16INK4a reaction. The case became squamous cell carcinoma later (Fig. 2d). The expression of p16INK4a was more prominent in the basal layer than in the surface layer in inverted papillomas. HPV-16 with mixed integration was detected in this case. Bar = 200 μm. d: Metachronous squamous cell carcinoma that recurred after primary surgery for inverted papilloma (c). The invasive carcinoma cells displayed stronger p16INK4 expression compared with the inverted papilloma (c). HPV-16 was also detected with mixed integration. Bar = 200 μm. e: Inverted papilloma with negative p16INK4a reaction. This case had HPV-33 infection. Bar = 200 μm. f: Inverted papilloma with negative p16INK4a reaction. The human papillomavirus genome was not identified in this case. Bar = 200 μm