Introduction: Anus-preserving surgery for a large rectal gastrointestinal stromal tumor (GIST) may be difficult because of the location of the tumor in the pelvis. Therefore, rectal GIST might require extensive surgery, such as abdominoperineal resection. In recent years, preoperative imatinib therapy has been used to reduce tumor size and preserve the anus in some cases. However, there have been few reports of laparoscopic anal-preserving surgery for giant rectal GIST. Presentation of a case: We present the case of a 55-year-old man who was referred to our hospital for examination of a 10-cm pelvic mass in the lower rectum. Endoscopic ultrasound with fine needle aspiration was performed, and the pathological findings resulted in a diagnosis of GIST. The mass had spread to the prostate and left levator ani muscles, and as a result, surgery was deemed difficult to perform without damaging the pseudo-capsule. Therefore, preoperative chemotherapy with imatinib mesylate (IM) was performed for 8 months. The mass was reduced to 7.8 cm, and laparoscopic intersphincteric resection (ISR) was performed. Discussion: We also review prior cases of rectal GIST where patients had undergone anal-preserving surgery following preoperative chemotherapy with IM. Our case represented the largest tumor size in a review of cases of patients who had successful anal-preserving laparoscopic surgery following preoperative chemotherapy with IM. Conclusion: Preoperative chemotherapy with imatinib mesylate was effective for reducing the rectal GIST, and laparoscopic ISR was useful for anal preservation, even when a tumor is large.
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