Purpose: Understanding the muscular structure of the anal canal is crucial for the diagnosis and treatment of anorectal diseases. Treitz muscle is a vital yet poorly understood component. It supports the anal venous plexus and contributes to anal cushion formation. However, its anatomical details remain unclear, and various theories suggest different origins for its muscle bundles, which affects our understanding of the pathophysiology of hemorrhoids. In this study, we sought to clarify the origin and localization of Treitz muscle to provide an anatomical foundation for understanding anal function. Methods: In this descriptive cadaveric study of 11 cadavers, we performed macroscopic examinations and immunohistological analyses on tissues from the anterior, lateral, and posterior walls of the anal canal. The origin and localization of Treitz muscle were qualitatively evaluated. Results: Treitz muscle is a smooth muscle formed by a directional change in the muscle bundles of the internal anal sphincter, running longitudinally along its surface. A shift in the direction of muscle bundles originating from the internal anal sphincter, giving rise to Treitz muscle, was frequently observed in the anterolateral wall of the anal canal. Conclusion In summary, Treitz muscle, a smooth muscle extending from the internal anal sphincter, is considered part of the muscularis propria. Its directional shift was localized to the anterolateral wall, indicating that Treitz muscle is not uniformly distributed around the anal canal. This site-specific localization may influence the risk of hemorrhoids or cancer invasion depending on its anatomical position.

Background:Capecitabine and irinotecan combination therapy (XELIRI) has been examined at various dose levels to treat metastatic colorectal cancer (mCRC). Recently, in the Association of Medical Oncology of the German Cancer Society (AIO) 0604 trial, tri?weekly XELIRI plus bevacizumab, with reduced doses of irinotecan (200mg/m2 on day 1) and capecitabine (1600mg/m2 on days 1–14), repeated every 3weeks, has shown favorable tolerability and effcacy which were comparable to those of capecitabine and oxaliplatin (XELOX) plus bevacizumab. The doses of capecit?abine and irinotecan in the AIO trial are considered optimal. In a phase I/II study, XELIRI plus bevacizumab (BIX) as second?line chemotherapy was well tolerated and had promising effcacy in Japanese patients. Methods:The Asian XELIRI ProjecT (AXEPT) is an East Asian collaborative, open?labelled, randomized, phase III clinical trial which was designed to demonstrate the non?inferiority of XELIRI with or without bevacizumab versus standard FOLFIRI (5?lfuorouracil, leucovorin, and irinotecan combination) with or without bevacizumab as second?line chemo?therapy for patients with mCRC. Patients with 20years of age or older, histologically conifrmed mCRC, Eastern Coop?erative Oncology Group performance status 0–2, adequate organ function, and disease progression or intolerance of the ifrst?line regimen will be eligible. Patients will be randomized (1:1) to receive standard FOLFIRI with or with?out bevacizumab (5mg/kg on day 1), repeated every 2weeks (FOLIRI arm) or XELIRI with or without bevacizumab (7.5mg/kg on day 1), repeated every 3weeks (XELIRI arm). A total of 464 events were estimated as necessary to show non?inferiority with a power of 80% at a one?sided α of 0.025, requiring a target sample size of 600 patients. The 95% conifdence interval (CI) upper limit of the hazard ratio was pre?speciifed as less than 1.3. Conclusion:The Asian XELIRI ProjecT is a multinational phase III trial being conducted to provide evidence for XELIRI with or without bevacizumab as a second?line treatment option of mCRC.