Intramucosal adenocarcinoma of the stomach

by Jason Wasserman MD PhD FRCPC
March 13, 2025

Intramucosal adenocarcinoma is an early-stage cancer of the stomach that starts from glandular cells within the innermost layer of the stomach lining (the mucosa). The term “intramucosal” means the cancer cells are found only within this mucosal layer and have not spread into deeper layers of the stomach wall.

What are the symptoms of intramucosal adenocarcinoma?

Intramucosal adenocarcinoma of the stomach often causes few or no symptoms because it is usually found at an early stage. However, if symptoms occur, they might include:

• Indigestion or heartburn.
• Mild stomach discomfort or pain.
• Nausea or loss of appetite.
• Bloating after eating.
• Unexplained weight loss.

What causes intramucosal adenocarcinoma?

Intramucosal adenocarcinoma is often related to long-term inflammation of the stomach lining (chronic gastritis). Common causes include infection by a bacteria called Helicobacter pylori (H. pylori), dietary factors (such as high intake of salty, smoked, or processed foods), smoking, and genetic factors.

What is the difference between intramucosal adenocarcinoma and invasive adenocarcinoma?

The main difference is how deeply the cancer has grown into the stomach wall. Intramucosal adenocarcinoma is limited strictly to the innermost mucosal layer and does not invade beyond a thin layer called the muscularis mucosae. In contrast, invasive adenocarcinoma spreads deeper, penetrating through the muscularis mucosae into underlying muscle or connective tissue layers, making it more likely to spread to other body parts.

How is this diagnosis made?

The diagnosis of intramucosal adenocarcinoma is typically made after examining a biopsy (a small tissue sample) taken during an endoscopy. An endoscopy is a procedure where a doctor inserts a thin tube with a camera into your stomach to visually inspect the lining and collect tissue samples.

What does intramucosal adenocarcinoma look like under the microscope?

Under the microscope, intramucosal adenocarcinoma appears as abnormal glandular cells confined strictly within the mucosal layer. Pathologists look for changes such as cells growing irregularly, crowding together, and showing abnormal shapes and sizes. Importantly, these cancer cells have not spread deeper into the muscle or connective tissue layers of the stomach wall.

Histologic grade

Intramucosal adenocarcinoma of the stomach is typically divided into three grades – well differentiated, moderately differentiated, and poorly differentiated. The grade is based on the percentage of the tumour cells forming round structures called glands. A tumour that does not create any glands is called undifferentiated. The grade is important because poorly differentiated and undifferentiated tumours tend to behave more aggressively. For example, these tumours are more likely to spread to lymph nodes and other body parts.

• Well differentiated: More than 95% of the tumour comprises glands. Pathologists also describe these tumours as grade 1.
• Moderately differentiated: 50 to 95% of the tumour comprises glands. Pathologists also describe these tumours as grade 2.
• Poorly differentiated: Less than 50% of the tumour comprises glands. Pathologists also describe these tumours as grade 3.
• Undifferentiated: Very few glands are seen anywhere in the tumour.

Lymphovascular invasion (LVI)

Lymphovascular invasion means that cancer cells are found inside tiny blood vessels or lymphatic vessels within the stomach tissue. This finding suggests the potential for the cancer to spread to other areas of the body.

Perineural invasion (PNI)

Perineural invasion means that cancer cells are seen surrounding or invading nerves in the stomach tissue. Like lymphovascular invasion, this indicates that the tumour may have a higher risk of spreading.

Margins

A margin refers to the edge of tissue removed during surgery. Pathologists closely examine margins to ensure no cancer cells are present at these edges. Clear margins (no cancer cells at the edges) indicate that the cancer has been entirely removed, reducing the risk of recurrence.

What stage is intramucosal adenocarcinoma?

Intramucosal adenocarcinoma is typically classified as Stage IA, the earliest stage of stomach cancer, according to the TNM staging system. This stage indicates that the cancer is limited to the innermost lining and has not spread to deeper layers or lymph nodes.

What is the prognosis for someone diagnosed with intramucosal adenocarcinoma?

The prognosis for intramucosal adenocarcinoma is generally excellent because it is detected early. With proper treatment, often involving removal of the affected area, most patients have a very high chance of full recovery, and the risk of cancer returning or spreading is low.