Inflammatory Pseudotumor of the Anal Canal Mimicking Colorectal Cancer: Case Report and Hints to Improve a Patient’s Fitness for Treatment and Prevention

<b>Background and Clinical Significance:</b> Men who engage in anal fisting may experience full rectal and colon thickness injury resulting in an endoscopic emergency. The endoscopist does not routinely question patients about their sexual habits, nor are patients compliant with counseling during the endoscopy procedure as indicated by the infectious disease clinician. <b>Case Presentation:</b> A 47-years-old HIV- and monkeypox virus (MPXV)-negative Caucasian gay man underwent colonoscopy because of changes in bowel habits with anal discomfort and rectal bleeding. The first colonoscopy showed a vegetative annular neoformation of the anal canal. There was a concentric stenosis of the lumen. The endoscopist suspected the diagnosis of anal squamous cell carcinoma and a histopathology investigation was requested. Biopsy histology excluded a frank neoplasm or anal intraepithelial neoplasia (AIN). Then, the patient was referred to a multidisciplinary team. With adequate counseling, the patient disclosed his habitual anal fisting. Laboratory identification of L1-L3 <i>Chlamydia trachomatis</i> (CT) genovars was positive for CT L1, L2, real-time PCR for <i>Neisseria gonorrhoeae</i> (NG), and <i>Mycoplasma hominis</i>. Human Papillomavirus (HPV)-DNA detection identified HPV type 70, 68, and 61. We illustrate this case with plenty of histology and immunohistochemistry. We also review the differential diagnosis of AIN according to the 5th edition (2019) WHO Classification of Digestive System Tumours. <b>Conclusions:</b> Our patient emphasizes two important aspects of endoscopy and pathology: first, the significance of understanding patients' sexual behaviors in diagnosing rectal and colon injuries, as well as the need for sexually transmitted infections (STI) screening especially for CT; and second, the effectiveness of a multidisciplinary communication model that encourages private discussions to alleviate patients' fears and improve prevention efforts.