Surreal digital illustration symbolizing hidden submucosal tumors in colon cancer detection.

Uncommon Colon Cancer: When a Submucosal Tumor Isn't What It Seems

Theo Raines monogram
Theo Raines in Health & Wellness October 2026 • 3 min read.

"A rare case highlights the challenges in diagnosing adenocarcinoma hidden beneath the colon's surface."


Colonoscopies are a routine procedure for detecting abnormalities in the colon, often leading to the discovery of polyps or tumors. Most of these findings are straightforward, but sometimes, what appears to be a simple submucosal tumor (SMT) can turn out to be something far more complex.

A recent case published in the medical literature highlights just such a scenario, where a 64-year-old woman underwent a colonoscopy for abdominal discomfort, revealing a small, protruded lesion initially diagnosed as an SMT. However, the subsequent pathological examination revealed a hidden adenocarcinoma, challenging the initial diagnosis and underscoring the importance of thorough investigation.

This article delves into the details of this unusual case, exploring the diagnostic challenges and the lessons learned about the subtle nature of colon cancer.

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The National Burden

The CDC reports that colorectal cancer is the fourth most common cancer in men and women, excluding some types of skin cancer. It is also the fourth leading cause of cancer-related deaths in the United States. Federal cancer data are used to track rates and trends, support research, measure prevention progress, address disparities, and improve outcomes.

Assessing and Removing Submucosal Lesions

Endoscopic submucosal dissection offers a curative, organ-preserving approach for early-stage gastrointestinal tumors, but its adoption remains inconsistent worldwide. Measuring submucosal invasion depth in T1 colorectal carcinoma can be difficult, creating a risk of inadequate or over-extensive treatment. Research on colorectal laterally spreading tumors has also compared different endoscopic treatment methods and their advantages and disadvantages.

From Depth to Tumor Evolution

Research on pT1 colorectal cancer established that microstaging invasive cancer requires attention to both the width and depth of submucosal invasion. Tumor budding at the advancing edge can further stratify metastatic risk into minimal, low, and high categories. Later evolutionary models described cancer as somatic evolution, including Nowell's influential proposal that tumors begin from a precursor cell with a growth advantage that undergoes clonal expansion.

The Unexpected Discovery: A Closer Look at the Case

Surreal digital illustration symbolizing hidden submucosal tumors in colon cancer detection.

The 64-year-old patient presented with typical abdominal discomfort, leading to a colonoscopy that detected a 10mm lesion in the descending colon. Visually, the tumor appeared to be covered by normal-appearing mucosa, leading to an initial diagnosis of a submucosal tumor. Adjacent to this, a small adenomatous polyp was also observed.

To accurately assess the SMT and address the coexisting polyp, doctors performed an endoscopic submucosal dissection (ESD) to remove both lesions. It was the subsequent pathological examination that revealed the surprising truth: the SMT was, in fact, a moderately differentiated tubular adenocarcinoma confined to the submucosal layer.

  • Initial Presentation: Abdominal discomfort led to a colonoscopy.
  • Lesion Discovery: A 10mm protruded lesion was found, initially diagnosed as a submucosal tumor (SMT).
  • Coexisting Polyp: A small adenomatous polyp was present near the SMT.
  • Diagnostic Procedure: Endoscopic submucosal dissection (ESD) was performed to remove both lesions.
  • Unexpected Diagnosis: Pathological examination revealed the SMT to be a moderately differentiated tubular adenocarcinoma.
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Refining Endoscopic Treatment

Recent colorectal cancer research continues to examine lesions arising from uncontrolled cell growth in the colon, rectum, and appendix. A 2026 systematic review and meta-analysis is comparing endoscopic submucosal dissection with endoscopic mucosal resection for laterally spreading tumors larger than 20 mm. Its stated outcomes include local recurrence, while the comparative efficacy and safety of the two techniques remain controversial.

Where Certainty Breaks Down

The National Cancer Institute notes that signs and symptoms attributed to colon cancer may also result from other conditions. This limits the specificity of symptom-based reasoning alone. Separately, long-term outcomes after endoscopic or surgical resection of submucosal invasive colorectal cancer have been described as insufficiently known in retrospective research.

Further complicating the case, the adenocarcinoma was completely covered by non-neoplastic mucosa, and the coexisting polyp was identified as a tubular adenoma. Histological analysis showed no continuity between the adenocarcinoma and the adenoma, adding another layer of complexity to the diagnosis.

Key Takeaways: What This Case Teaches Us

This rare case underscores the challenges in diagnosing colon cancer and the importance of thorough pathological examination, even when initial assessments suggest a benign condition. It serves as a reminder that not all tumors are what they seem on the surface, and vigilance is key to early and accurate diagnosis.

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When Local Excision Is Enough

Submucosally invasive colorectal carcinoma, or pT1 disease, can potentially be cured by local excision. The cited pathology summary says that surgical intervention in the United States is reserved for tumors with high-grade morphology, lymphovascular invasion, and close or positive margins. It also reports that Japanese practice recommends surgery in additional situations, including mucinous tumors, tumors with 41000 μm of submucosal invasion, and tumors with high-risk features.

More Precise Lesion Selection

Future endoscopic care is centered on accurately assessing lesion morphology, optical pattern, and invasion depth. These assessments help determine whether endoscopic mucosal resection, endoscopic submucosal dissection, or another treatment is appropriate. New technologies such as EndoSCell® are also being described for precise intraoperative identification of tumor cells, with the stated goal of lowering rectal-cancer recurrence and improving anal preservation.

The Shift to Precision Stratification

The 2025 annual review characterizes systemic colorectal cancer management as undergoing a pivotal evolution. Therapeutic decisions are shifting from traditional anatomic staging toward precision stratification based on tumor molecular biology. The review also describes dynamic management guided by molecular profiling.

Evidence From Everyday Care

A 2024 study examined how real-world evidence can responsibly inform treatment selection. Using real-world data, randomized controlled-trial evidence, and expert consensus as validation points, the researchers identified an existing adjuvant chemotherapy guideline for stage II and III colon cancer. The example shows how routine clinical data can help evaluate treatment decisions outside controlled trials.

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

Everything You Need To Know

1

What is a submucosal tumor (SMT) in the context of a colonoscopy, and why might it be cause for concern?

A submucosal tumor (SMT) is a lesion found beneath the inner lining of the colon, often appearing as a protruded mass during a colonoscopy. While some SMTs are benign, this case demonstrates that what appears to be an SMT can sometimes mask a more serious condition, such as a hidden adenocarcinoma. The concern arises because the overlying normal-appearing mucosa can obscure the presence of underlying cancerous cells, making accurate diagnosis challenging without thorough pathological examination. The implication is that visual assessment during a colonoscopy alone isn't always sufficient for a definitive diagnosis.

2

How was the unexpected adenocarcinoma discovered in this particular case, and what does it highlight about colon cancer detection?

The adenocarcinoma was unexpectedly discovered through a pathological examination following an endoscopic submucosal dissection (ESD) of a lesion initially diagnosed as a submucosal tumor (SMT). The 64-year-old patient underwent a colonoscopy due to abdominal discomfort, which revealed the SMT and a small adenomatous polyp. Both lesions were removed via ESD, and the subsequent microscopic analysis revealed that the 'SMT' was actually a moderately differentiated tubular adenocarcinoma. This case highlights the limitations of relying solely on visual assessment during colonoscopies and underscores the critical importance of histological analysis for accurate colon cancer detection, even when the surface appears normal.

3

What is endoscopic submucosal dissection (ESD), and why was it used in this specific colon cancer case?

Endoscopic submucosal dissection (ESD) is an advanced endoscopic technique used to remove lesions from the gastrointestinal tract, including the colon. In this case, ESD was performed to remove both the lesion initially diagnosed as a submucosal tumor (SMT) and a coexisting adenomatous polyp. ESD allows for the complete removal of lesions, enabling thorough pathological examination, which was crucial in revealing the hidden adenocarcinoma. The importance of ESD lies in its ability to provide a more detailed tissue sample than a simple biopsy, increasing the chances of detecting subtle or unexpected cancerous changes.

4

What does it mean for an adenocarcinoma to be 'completely covered by non-neoplastic mucosa,' and why does this complicate diagnosis?

When an adenocarcinoma is completely covered by non-neoplastic mucosa, it means that the cancerous cells are hidden beneath a layer of normal-appearing tissue. This complicates diagnosis because the visual appearance during a colonoscopy may be misleading, as the surface of the colon appears healthy. In this specific case, the adenocarcinoma was masked by this normal mucosa, leading to an initial misdiagnosis of a submucosal tumor (SMT). This emphasizes the need for pathological examination of removed lesions, even if they appear benign during the colonoscopy.

5

What are the key takeaways from this case regarding the diagnosis and treatment of unusual colon cancers, and what implications might it have for future screenings?

The key takeaways are that colon cancers can present in unusual ways, such as adenocarcinomas mimicking submucosal tumors (SMTs), and that thorough pathological examination is crucial for accurate diagnosis. This case underscores that visual assessment during colonoscopies alone is not always sufficient and that even lesions appearing benign should be biopsied or removed for histological analysis. For future screenings, this highlights the need for heightened vigilance, especially when encountering SMT-like lesions, and consideration of advanced techniques like endoscopic submucosal dissection (ESD) to ensure complete removal and thorough examination of suspicious areas. It may also prompt further research into imaging techniques that can better visualize abnormalities beneath the mucosal surface.

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