EP324 - Pregnancy and Rectal GIST: Case Report on Long-Term Surveillance & Recurrence with LLN Metastasis Managed by Imatinib and Robotic Surgery

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Purpose/Background: Rectal gastrointestinal stromal tumors (GISTs) are rare, comprising approximately 5% of all GISTs and only 0.1% of rectal tumors. These tumors often present at a more advanced stage compared to GISTs in other locations, due to their uncommon occurrence in the rectum and the challenging anatomy of this location. Lymph node metastasis is exceedingly rare in GISTs, including rectal GISTs, with the liver and peritoneum being more common sites of metastatic spread. Diagnosis typically involves imaging modalities such as colonoscopy, MRI, and biopsy with immunohistochemical confirmation of CD117 positivity. Surgical resection remains the cornerstone of treatment, with complete resection and histologically negative margins being critical for a curative outcome.
Long-term surveillance is essential due to the risk of recurrence. Tyrosine kinase inhibitors like Imatinib have significantly improved recurrence-free survival rates, particularly in high-risk patients.

Methods/Interventions: In this case report, we retrospectively review the management of a woman with a lower rectal GIST in the rectovaginal septum. We present the case of a 29-year-old female who was incidentally found to have a very low rectal GIST during vaginal delivery. The tumor, located 4 cm from the anal verge and measuring 4x2 cm, was asymptomatic. Sigmoidoscopy confirmed the submucosal mass, and a tru-cut biopsy identified a high-grade GIST (G2) (8 mitoses/50 high-power fields). The patient was started on neoadjuvant Imatinib, 400 mg daily for four months, resulting in tumor reduction from 48x47 mm to 27x24 mm. She subsequently underwent successful transanal resection, with postoperative histopathology revealing a 40x35x20 mm mass, G1 histological grade (less than 5 mitoses/50 HPF), pT2 stage, negative margins, and CD117 positivity. Following surgery, the patient received adjuvant Imatinib for 3 years. A TEP scan at the end of the treatment period was normal.
Five years later, during a routine follow-up, the primary surgeon detected a recurrence on digital rectal examination, revealing a 1 cm mass. The patient, who was pregnant at the time, was managed with transanal surgical resection 2 months after cesarean section delivery. The postoperative histopathology report revealed a 15 mm mass classified as high-grade GIST (G2) (29 mitoses/50 HPF), pT1 stage, with negative surgical margins and CD117 positivity. The patient was restarted on Imatinib for 5 years and followed with annual TEP scans.

Results/Outcomes: Six years after the second resection, a TEP scan showed a lesion in the left lateral internal iliac lymph node, which a CT-guided biopsy confirmed as GIST. The patient underwent robotic lateral lymph node dissection (LLNPD), and lymph node histopathology confirmed recurrent GIST.

Conclusion/Discussion: This case underscores the importance of long-term surveillance for rectal GIST patients, given the potential for late recurrences even after initially successful treatment. The complexities of managing GIST during pregnancy and recurrent disease highlight the need for a multidisciplinary approach. Early detection through routine imaging and timely surgical intervention is critical for managing recurrent GIST and optimizing patient outcomes. An important question remains: how long should Imatinib be used to minimize the risk of recurrence in high-risk patients, and what factors should guide the duration of therapy?