Tumor Deposit: Definition

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A tumor deposit is a separate cancerous nodule in the fat near a tumor. It contains no lymph node tissue, blood vessels, or nerves. Pathologists report tumor deposits most often in colorectal cancer, where they affect the stage.

This article explains what a tumor deposit is, how it affects the stage, and what your report may say.

What is a tumor deposit?

A tumor deposit is a small island of cancer separate from the main tumor. In colorectal cancer, it lies in the fat around the bowel—this fat drains lymph from the tumor. Under the microscope, the pathologist cannot find any lymph node tissue, vessel wall, or nerve inside it. The nodule can be large enough to see or visible only under the microscope. Its size and shape do not matter.

A tumor deposit is a form of spread. Cancer cells have moved from the main tumor into nearby fat. However, a tumor deposit is different from cancer that has spread to a distant organ, such as the liver or lungs. Doctors call distant spread metastasis.

How do pathologists tell a tumor deposit from other findings?

A nodule of cancer in the fat near the tumor can have several causes. The pathologist looks carefully at what surrounds the cancer cells:

Lymph node metastasis. If the nodule contains lymph node tissue, it is a positive lymph node.
Vascular invasion. Sometimes the pathologist can see the wall of a vein around the cancer. The cancer is then growing inside a vessel. See vascular invasion.
Perineural invasion. If the cancer surrounds a nerve, it is perineural invasion.
Tumor deposit. Only when none of these structures is present does the pathologist call the nodule a tumor deposit.

Pre-surgical treatment can make this harder. After chemotherapy or radiation, a separate nodule may remain from the main tumor rather than be a true deposit. Nodules separated from the tumor only by scar tissue do not count as deposits.

How do tumor deposits affect the stage?

Tumor deposits affect the N category of the TNM stage in colorectal cancer. They do not change the T category. The rules are:

No lymph nodes with cancer. Sometimes all the nodes are negative, but tumor deposits are present. The nodal stage is then pN1c. See nodal stage.
Lymph nodes with cancer. If any lymph node contains cancer, the N category depends on the number of positive nodes. The pathologist does not include tumor deposits in that count.

In both cases, the pathologist records the number of tumor deposits in the report.

Why are tumor deposits important?

Tumor deposits show that the cancer has started to spread beyond the main tumor. They link to a higher risk that the cancer will come back. This holds even when all lymph nodes are negative. When a report shows a pN1c stage, doctors generally consider chemotherapy after surgery. Your oncologist will explain what the finding means for you.

Do reports use the term for other cancers?

The formal definition of a tumor deposit comes from the staging rules for colorectal cancer. Some reports use the term more loosely to describe a group of cancer cells found away from the main tumor. If your report uses the term for another cancer, ask your doctor what it means in that setting.

What might my report say about tumor deposits?

Reports describe tumor deposits in a few standard ways. Each laboratory phrases them a little differently:

Tumor deposits present. The pathologist found one or more deposits. The report usually gives the number.
Tumor deposits not identified. The pathologist found no deposits.
pN1c. Tumor deposits are present, and no lymph nodes contain cancer.
The lymph node count with deposits is listed separately. For example, “2 of 18 lymph nodes positive; tumor deposits present (number: 3).”

Questions to ask your doctor

Did my report find any tumor deposits?
How many tumor deposits were there?
Did any lymph nodes contain cancer?
What is my nodal stage?
Do the tumor deposits change my treatment plan?
Will I need chemotherapy after surgery?
How will you watch for the cancer coming back?