| Summary: | Objective: To examine the association between human papillomavirus (HPV) infection and penile cancer among Japanese patients. Methods: Thirty-four patients with penile cancer were enrolled in this study. DNA was extracted from paraffin-embedded tumor tissue samples, and HPV-DNA tests and genotyping were performed. For all of the samples, in situ hybridization (ISH) was performed to locate HPV-DNA in tumor tissue. Furthermore, expression levels of p16-INK4a, mini-chromosome maintenance protein 7 (mcm-7), HPV-L1, and Ki-67 were analyzed using immunohistochemical methods. Results: HPV and high-risk (HR)-HPV were detected in 14 (41.1%; 95% confidence interval (CI) 24.6–57.7%) and 12 (35.2%; 95% CI 19.2–51.4%) cases, respectively. HPV16 was the most frequently detected HPV type. Among the HR-HPV-positive cases, a punctate HR-HPV-DNA signal pattern was detected by ISH in tumor cell nuclei. P16-INK4a was expressed in 66.7% (95% CI 42.8–90.1%) of HR-HPV-positive cases and was significantly more frequent and stronger in HR-HPV-positive cases than in HPV-negative cases. There was no significant difference in the occurrence or distribution of mcm-7 or Ki-67 expression between HPV-positive and HPV-negative cases. HPV-L1 expression was not observed in any of the cases examined. Conclusions: HPV infection may have had an etiological role in 41% of the examined cases of penile cancer in Japan. Keywords: Penile cancer, Human papillomavirus, p16-INK4a, Mini-chromosome maintenance protein 7, Ki-67
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