Surgical management challenges of ultra-low rectal GIST: oncologic safety versus functional preservation: A Case Report

Authors

Abstract

IntroductionRectal gastrointestinal stromal tumors (GISTs) represent <5% of all GISTs. Tumors located very close to the dentate line pose a challenge because radical surgery may impair anorectal function.
Case PresentationA 25-year-old male presented with altered bowel habits. Examination revealed a mobile mass 3-4 cm from the anal verge. Endoanal ultrasound showed a 28 × 35 mm lesion originating from the muscularis propria without sphincter invasion. The patient underwent sphincter-preserving transanal local excision. R0 resection was achieved. According to Armed Forces Institute Of Pathology (AFIP) criteria, the tumor was classified as intermediate risk. Adjuvant imatinib (400 mg/day) was initiated. The patient was discharged on postoperative day 4 and remains disease-free at 3 months.
ConclusionIn selected ultra-low rectal GISTs, transanal excision can achieve oncologic safety while preserving sphincter function.

Keywords

Introduction

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal system and originate from interstitial Cajal cells.¹ It is most commonly found in the stomach (60-70%) and small intestine (20-30%), while rectal involvement accounts for less than 5% of all cases.² Rectal GISTs pose unique clinical challenges in terms of diagnosis and treatment due to their rarity and anatomical location.^3,4
In tumors located in the distal segment of the rectum, particularly those near the dentate line (ultra-low), proximity to the anal sphincters complicates surgical planning. Radical surgical approaches in this region (e.g., abdominoperineal resection) may result in the need for a permanent stoma and functional losses.⁴ In contrast, local excision techniques preserve the sphincter but require careful patient selection to ensure oncological safety.⁵
It has been reported that rectal GISTs may exhibit more aggressive biological behavior compared to gastric GISTs.6 Risk classification is based on tumor size, mitotic index, and location, and rectal tumors should be evaluated with particular caution in terms of high-risk categories.² Current guidelines recommend adjuvant imatinib therapy in moderate- and high-risk cases.^6,7
Ensuring oncological safety with sphincter-preserving surgery and the adjuvant treatment decision process in ultra-low localized rectal GISTs have been addressed in a limited number of studies in the literature.^4,5 In this case presentation, the surgical and adjuvant treatment management of a rectal GIST located very close to the dentate line in a young patient is discussed.

Case Presentation

A 25-year-old male patient was evaluated at another center for complaints of changes in bowel habits and was referred to our center after examinations revealed a submucosal mass in the rectum. A mass was palpated approximately 3-4 cm proximal to the anal verge during the physical examination of the patient with no specific findings in their medical history. The mass was mobile and did not cause ulceration or indentation in the overlying mucosa. Laboratory tests showed that blood count and biochemical parameters were within normal limits.
Endoanal ultrasound (ERUS) revealed a heterogeneous echogenic lesion measuring approximately 28 × 35 mm in size on the anterior wall of the rectum, at the 7–12 o'clock position, thought to originate from the muscularis propria. The lesion was not associated with the sphincters, and no signs of invasion were observed. Gastrointestinal stromal tumor (GIST) was considered as a preliminary diagnosis.
A soft tissue mass measuring approximately 4.5 × 3.5 cm, was observed in the dynamic contrast-enhanced abdominal computed tomography scan (CT), protruding into the lumen of the anterior wall of the rectum, with indistinct borders from the prostate. The lesion showed minimal contrast enhancement, consistent with a mesenchymal tumor. No distant metastases were detected (Figure 1).
The patient was evaluated by a multidisciplinary team, and sphincter-preserving surgery was planned. Under general anesthesia, in the lithotomy position, the mucosa surrounding the lesion immediately proximal to the dentate line was opened via a transanal approach, and the approximately 4 cm diameter mass was excised without damaging the muscular layer. After bleeding was controlled, the mucosal defect was primarily sutured (Figure 2).
Histopathological examination revealed a spindle cell tumor proliferation located within the muscularis propria. The tumor measured 4 cm in diameter, and 10 mitoses were detected in 50 high-power fields. No necrosis, ulceration, or tumor rupture was observed. Immunohistochemical examination revealed that tumor cells were positive for CD117, DOG1, and CD34; negative for SMA, desmin, and S-100. The Ki-67 proliferation index was assessed as 1–2%. Surgical margins were negative (R0 resection). The risk grade was classified as 2 according to AFIP criteria.
The postoperative period was uneventful, and the patient was discharged on the postoperative 4th day. Following a multidisciplinary evaluation, adjuvant imatinib (400 mg/day) therapy was initiated and planned for 3 years. The patient remains disease-free at the 3-month follow-up.
Ethical ApprovalThis study did not require ethical approval according to the relevant guidelines. But written informed consent was obtained from the patient for publication of this case report and accompanying images
Reporting GuidelinesThis case report is presented in accordance with the CARE guidelines.

Discussion

Rectal gastrointestinal stromal tumors account for less than approximately 5% of all GIST cases and constitute a distinct clinical subgroup from a surgical and oncological perspective due to their anatomical localization.^2,3 The narrow anatomical structure of the pelvis and its proximity to the anal sphincter complex complicate surgical planning and require careful evaluation of functional outcomes.³ Localization-related prognostic differences have been reported in the literature, and gastric GISTs have been shown to have a better prognosis than intestinal GISTs of similar size and mitotic activity.⁷ Therefore, rectal localization should be considered independently in risk assessment.
The primary goal of surgical treatment for rectal GISTs is to achieve negative surgical margins (R0), and lymph node dissection is not routinely recommended.⁴ However, radical surgical approaches, particularly abdominoperineal resection, may result in a permanent stoma in tumors located very close to the dentate line.⁴ Sphincter preservation is particularly important for quality of life in young patients. In recent years, it has been reported that transanal local excision and minimally invasive techniques can provide oncologically acceptable results in selected cases.⁸
In our case, the tumor diameter was 4 cm, and 10 mitoses were detected in a 50x magnification field. According to the AFIP classification, the risk grade was assessed as 2.2 However, the literature indicates that local recurrence rates in rectal GISTs may be higher than in gastric GISTs, and therefore the risk category should be interpreted with caution.⁷ Although negative surgical margins are a positive factor in terms of local control, increased mitotic activity has been decisive in the adjuvant treatment decision.
Randomized studies have demonstrated that adjuvant imatinib therapy reduces the risk of recurrence in intermediate- and high-risk GISTs.6 It has been reported that adjuvant therapy administered for 3 years provides superior results compared to 1 year.⁶ Current ESMO guidelines recommend adjuvant imatinib therapy based on risk assessment.7 Accordingly, following a multidisciplinary assessment, the patient was started on adjuvant imatinib for a period of 3 years.
In this case, preoperative imaging revealed a lesion originating from the muscularis propria and adjacent to the prostate, but no sphincter invasion was detected. This situation indicated that an organ-preserving approach might be possible. Achieving R0 resection with transanal excision has provided an important advantage in terms of preserving functional integrity. Although no recurrence was detected during the three-month short-term follow-up, long-term close monitoring is necessary for rectal GISTs.⁷
Learning Points1. Although rectal GISTs are rare, surgical planning is critically important for functional outcomes in cases of distal localization.
2. In cases with ultra-low localization, sphincter-preserving transanal excision may be oncologically safe with appropriate patient selection.
3. Tumor size and mitotic index are decisive in risk classification, and rectal localization should be carefully evaluated in terms of prognosis.
4. The decision to use adjuvant imatinib should be made using a multidisciplinary approach.

Limitations

This report has several limitations inherent to single case reports. The findings cannot be generalized to all patients with ultra-low rectal gastrointestinal stromal tumors. In addition, the follow-up period in this report is relatively short, and long-term oncological outcomes cannot yet be evaluated. Further studies with larger patient series and longer follow-up periods are required to better define optimal treatment strategies for ultra-low rectal GISTs.

Conclusion

Ultra-low-lying rectal gastrointestinal stromal tumors present significant surgical challenges due to their rarity and proximity to the anal sphincter complex. This case demonstrates that sphincter-preserving transanal excision can be performed without compromising oncological safety with appropriate patient selection. However, risk stratification should be performed considering tumor size, mitotic activity, and localization, and the decision for adjuvant therapy should be made through multidisciplinary evaluation. Long-term follow-up in rectal GISTs is of great importance, particularly in terms of recurrence risk.

Declarations

Abbreviations

AFIP: armed forces institute of pathology
CARE: case report guidelines
CT: computed tomography
ERUS: endorectal ultrasound
GIST: gastrointestinal stromal tumor
HPF: high power field
R0: microscopically margin-negative resection

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