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 in Health & Wellness December 2025 • 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.

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.

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.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

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.

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.

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.

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.

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.