A rare cause of subepithelial tumor in the rectum

Yong Bo Park; Dong Hoon Baek

doi:10.5946/ce.2025.445

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Boost Your Learning with Quiz A rare cause of subepithelial tumor in the rectum: Yong Bo Park, Dong Hoon Baek; Clinical Endoscopy 2026;59(2):320-322.
DOI: https://doi.org/10.5946/ce.2025.445
Published online: March 9, 2026

Division of Gastroenterology, Department of Internal Medicine, Pusan National University School of Medicine and Biomedical Research Institute, Pusan National University Hospital, Busan, Korea

Correspondence: Dong Hoon Baek Division of Gastroenterology, Department of Internal Medicine, Pusan National University School of Medicine and Biomedical Research Institute, Pusan National University Hospital, 179 Gudeok-ro, Seo-gu, Busan 49241, Korea E-mail: dhbeak77@gmail.com

• Received: December 7, 2025 • Revised: December 29, 2025 • Accepted: December 30, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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A 61-year-old male patient without any unusual symptoms underwent a colonoscopy as part of a routine health examination. During the procedure, an 8-mm, smoothly elevated lesion was identified in the distal rectum, approximately 2 cm above the anal verge. The lesion was initially suspected to be a subepithelial tumor (SET), and the patient was referred to the gastroenterology department of our institution for further evaluation. The patient was in good general condition. Laboratory testing, including tumor markers, revealed values within normal limits: carcinoembryonic antigen 2.1 ng/mL, carbohydrate antigen 19-9 15.70 U/mL, and prostate-specific antigen 0.006 ng/mL. He denied any significant past medical or surgical history, and no relevant familial predisposition to malignancy was noted.

Colonoscopy at our institution confirmed a smoothly elevated lesion located approximately 2 cm above the anal verge (Fig. 1). To further characterize the lesion, endoscopic ultrasound was performed, which demonstrated a well-circumscribed hypoechoic mass confined to the second and third layers of the rectal wall. There was no evidence of perirectal or regional lymph node enlargement (Fig. 2). En bloc resection was subsequently performed via endoscopic mucosal resection with a ligation device (Fig. 3). Based on these findings, what is the most likely diagnosis?

Answer

Histopathologic examination of the resected specimen revealed a moderately differentiated adenocarcinoma measuring 0.8×0.4 cm, classified as pT1 with submucosal invasion of 1,900 μm out of a total submucosal thickness of 2,000 μm (Fig. 4). Notably, no additional high-risk histological features, such as lymphovascular invasion or tumor budding, were identified. After a comprehensive discussion with the patient regarding the risks and benefits of surgery, a decision was made to proceed with conservative management and close surveillance rather than additional surgical intervention. He has remained recurrence-free over a 4-year follow-up period.

Most SETs originate from the submucosal or muscularis propria layers of the gastrointestinal tract, whereas epithelial cell-derived malignancies, such as adenocarcinomas, originate from the mucosal epithelium.¹ This distinct origin typically results in differing endoscopic appearances: SETs usually present as smooth, elevated lesions with intact overlying mucosa, whereas epithelial cell-derived malignancies often exhibit mucosal surface abnormalities such as erosion, ulceration, or friability.²^,³ Consequently, mucosal patterns on endoscopy are key to differentiating true SETs from epithelial cell-derived malignancies.

However, rare cases of gastrointestinal adenocarcinomas that are entirely covered with a normal-appearing mucosa have been reported. To date, fewer than 10 cases of rectal adenocarcinoma completely covered by normal mucosa have been reported.⁴^-⁶ Similar cases have also been described in the esophagus and stomach.⁷^,⁸ Although the mechanism remains unclear, some hypotheses include vertical infiltration patterns, ectopic glandular origin, or growth along submucosal lymphovascular channels.⁹ Previous studies have shown that such tumors are often characterized by small size, poorly differentiated or mucinous histology, and a higher incidence of lymphovascular invasion and early metastasis. These features suggest that, despite their benign endoscopic appearance, these lesions may exhibit aggressive biological behavior.

In the present case, rectal adenocarcinoma was histologically confirmed from a lesion initially presumed to be a SET. This highlights that even small, smooth, and mucosa-covered lesions in the rectum may harbor malignancy. Therefore, if SETs with normal overlying mucosa are identified in the rectum, underlying adenocarcinoma must always be considered. Furthermore, given the potential for various malignancies arise as rectal SETs, complete endoscopic resection is mandatory.

Conflicts of Interest

The authors have no potential conflicts of interest.

Funding

This work was supported by a clinical research grant from the Pusan National University Hospital in 2026.

Author Contributions

Conceptualization: DHB; Data curation: all authors; Formal analysis: all authors; Investigation: all authors; Methodology: all authors; Supervision: DHB; Writing–original draft: YBP; Writing–review & editing: all authors.

Fig. 1.

Endoscopic appearance of a subepithelial rectal lesion. (A, B) Conventional white-light endoscopy reveals a small, smooth-surfaced elevated lesion located 2 cm above the anal verge. The overlying mucosa appears intact without erythema, erosion, or ulceration. (C) Narrow-band imaging with near focus shows a regular surface pattern and capillary network, with no evidence of pit pattern irregularity or microvascular distortion.

Fig. 2.

Endoscopic ultrasonographic (EUS) findings of the rectal lesion. (A) EUS using a mini-probe shows a well-demarcated, homogeneous hypoechoic lesion confined to the second and third layers of the rectal wall. (B) The lesion measures approximately 0.8 cm in maximal diameter on EUS.

Fig. 3.

Endoscopic mucosal resection (EMR-L) procedure and resected specimen. (A) The lesion is captured and lifted using a band ligation device (EMR-L) following submucosal injection. (B) Post-resection ulcer base following en bloc removal of the lesion. The resection site shows a clean mucosal defect with coagulated margins and no immediate signs of perforation or bleeding. (C) Gross view of the resected specimen.

Fig. 4.

Histopathologic findings of the resected rectal lesion. (A) Low-power view of the endoscopic mucosal resection specimen shows a moderately differentiated adenocarcinoma infiltrating the submucosal layer. The vertical resection margin is clear (hematoxylin and eosin [H&E] stain, ×40). (B) High-power view (H&E stain, ×100) highlights irregular glandular structures composed of atypical epithelial cells, consistent with moderately differentiated adenocarcinoma.

REFERENCES

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4. Sato K, Kojima Y, Matsuno Y, et al. A case of mucoid carcinoma of the sigmoid colon with features of a submucosal tumor. Nihon Shokakibyo Gakkai Zasshi 2011;108:88–94.PubMed
5. Shiraiwa S, Taniwaki S, Imamura T, et al. A case of rectal cancer presented as submucosal tumor without the continuation with the mucous membrane. Jpn J Gastroenterol 2014;75:749–753.Article
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9. Nakajima T, Kamano T, Shibasaki K, et al. Colonic carcinoma resembling submucosal tumor: report of a case and review of the literature. Int J Gastrointest Cancer 2005;36:155–161.Article PubMed

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A rare cause of subepithelial tumor in the rectum

Clin Endosc. 2026;59(2):320-322. Published online March 9, 2026

DOI: https://doi.org/10.5946/ce.2025.445

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A rare cause of subepithelial tumor in the rectum

Fig. 1. Endoscopic appearance of a subepithelial rectal lesion. (A, B) Conventional white-light endoscopy reveals a small, smooth-surfaced elevated lesion located 2 cm above the anal verge. The overlying mucosa appears intact without erythema, erosion, or ulceration. (C) Narrow-band imaging with near focus shows a regular surface pattern and capillary network, with no evidence of pit pattern irregularity or microvascular distortion.

Fig. 2. Endoscopic ultrasonographic (EUS) findings of the rectal lesion. (A) EUS using a mini-probe shows a well-demarcated, homogeneous hypoechoic lesion confined to the second and third layers of the rectal wall. (B) The lesion measures approximately 0.8 cm in maximal diameter on EUS.

Fig. 3. Endoscopic mucosal resection (EMR-L) procedure and resected specimen. (A) The lesion is captured and lifted using a band ligation device (EMR-L) following submucosal injection. (B) Post-resection ulcer base following en bloc removal of the lesion. The resection site shows a clean mucosal defect with coagulated margins and no immediate signs of perforation or bleeding. (C) Gross view of the resected specimen.

Fig. 4. Histopathologic findings of the resected rectal lesion. (A) Low-power view of the endoscopic mucosal resection specimen shows a moderately differentiated adenocarcinoma infiltrating the submucosal layer. The vertical resection margin is clear (hematoxylin and eosin [H&E] stain, ×40). (B) High-power view (H&E stain, ×100) highlights irregular glandular structures composed of atypical epithelial cells, consistent with moderately differentiated adenocarcinoma.