Abstract: 【Abstract】 Objective To analyze clinical and histopathological diagnoses of patients with solid tumors localized on the perianal and external genitalia regions, aiming to help clinicians correctly identify benign and malignant tumors. Methods A retrospective analysis was conducted on clinical, histopathological, and dermoscopic features, diagnosis and treatment of 389 patients diagnosed with solid tumors localized in the perianal and external genitalia regions in the Department of Dermatology, Peking University Third Hospital from January 2016 to May 2023. Results Among the 389 patients with solid tumors in perianal and external genitalia regions, 123 were males and 266 were females, with the age being 8 - 89 （41.86 ± 16.62） years. Based on the histological classification of skin tumors, melanocytic tumors were the most common type （33.16% ［129/389］）, followed by other tumors （21.59%, 84/389）, keratinocytic tumors （21.08%, 82/389）, soft tissue and neural tumors （13.62%, 53/389）, and appendageal tumors （10.54%, 41/389）. There were 83.03% （323/389） of benign tumors and 16.97% （66/389） of malignant tumors. Melanocytic nevus was the most common benign tumor, mostly involving the labia majora of females and mons pubis of males. Among the malignant tumors, squamous cell carcinoma was relatively common in females （40%, 10/25）, while extramammary Paget′s disease was relatively common in males （39.02%, 16/41）. The initial misdiagnosis rate of Bowenoid papulosis was the highest （11/11）, followed by squamous cell carcinoma （78.26%, 18/23） and basal cell carcinoma （40%, 4/10）; there was no significant difference in the initial misdiagnosis rate between different gender groups or different age groups（both P＞0.5）. A total of 367 patients underwent surgical excision under local anesthesia and all showed a good prognosis; the remaining 22 with malignant tumors were treated with photodynamic therapy, extended resection, free flap transfer, etc., and experienced no recurrence during the follow-up of 3 months to more than 3 years. Conclusions Solid tumors in the perianal and external genitalia regions were polymorphous, melanocytic tumors, keratinocytic tumors and other tumors accounted for a large proportion, while malignant tumors were relatively rare, and some were easily misdiagnosed. Most of the tumors in the regions had a good prognosis, without recurrence after the surgical resection.

Key words: Skin neoplasms, Skin manifestations, Pathologic processes, Perianus, External genitalia regions, Nature of tumors, Misdiagnosis