Background and Aims: Primary anorectal small-cell carcinoma (SCC) is a rare type of cancer, accounting for less than 1% of all anorectal tumors. Compared with common anorectal adenocarcinoma, the clinical symptoms and imaging manifestations of anorectal SCC are not specific, so the diagnosis is difficult, postoperative recurrence and distant metastasis are easy to occur, the prognosis is poor, and the overall mortality is extremely high. Due to the rarity and particularity of anorectal SCC, there are so far few domestic and foreign literature reports available, lack of relevant research data and treatment experience as well as in-depth understanding of its characteristics, and no unified optimal treatment plan, which bring certain troubles to clinical diagnosis and treatment. Here, the authors discuss the diagnosis and treatment modality of anorectal SCC through analyzing the diagnosis and treatment process in a treated case of primary anorectal SCC, so as to provide corresponding clinical experience and new ideas for the diagnosis and treatment of this condition.  
Methods: The clinical data of one patient with primary anorectal SCC were retrospectively analyzed. The patient's medical history, general condition, imaging examination, pathological tissue morphology and characteristics of immunomarker were analyzed and diagnosed, and corresponding treatment strategies were developed according to its characteristics, combined with review of relevant literature.
Results: The clinical feature of the patient presented was bloody stool, which was considered as anorectal malignant tumor after imaging examination, and SCC was pathologically suggested after twice colonoscopic biopsies. Then, laparoscopic-assisted Miles surgery was performed, and postoperative pathologic diagnosis was SCC of the anorectal canal. After operation, additional comprehensive treatment compromising pelvic radiotherapy and "cisplatin plus etoposide" EP chemotherapy regimen was applied. Regular reexaminations such as chest CT, total abdominal CT, pelvic MRI, colonoscopy, serum tumor markers showed no tumor recurrence or distant metastasis. The patient has survived with tumor-free status for 13 months by now, and was still in follow-up observation.
Conclusion: Primary anorectal SCC is a rare disease with low overall survival. The clinical symptoms and imaging manifestations of anorectal SCC are similar to those of common anorectal adenocarcinoma without specificity. Biopsy material is difficult to obtain under colonoscopy, and the diagnosis requires combining the histopathological findings and a variety of immunohistochemical markers. Surgical resection is the most important and effective method for the treatment of locally advanced anorectal SCC. Surgical treatment should be carried out as soon as possible. Postoperative combined treatment with pelvic radiotherapy and "cisplatin plus etoposide" EP chemotherapy regimen can improve the prognosis of patients and prolong their survival time.