Well differentiated

by Jason Wasserman MD PhD FRCPC
March 9, 2022

What does well differentiated mean?

Pathologists use the term well differentiated to describe a tumour made up of cells that look very similar to the normal, non-cancerous cells found in that area of the body. A tumour can be described as well differentiated based on the shape, size, and colour of the cells or by the way the cells stick together.

Why do pathologists use the word differentiated?

Pathologists use the word differentiated in their report because not all cancers look the same. Some cancers look very similar to normal, healthy cells while others look very different.

Pathologists commonly use five levels to describe these changes:

• Well differentiated – These cancers look very similar to the surrounding normal cells. In some cases it can be difficult for the a pathologist to tell the difference between the cancer and the normal cells.
• Moderately differentiated – The cells in these cancers are clearly abnormal looking but they still share some features with the surrounding normal cells.
• Poorly differentiated – These cancers look very abnormal. When the cells from a poorly differentiated tumour travel to a lymph node or other part of the body, additional tests such as immunohistochemistry may be required to determine the type of tumour and where it started. The movement of cancer cells to another part of the body is called metastasis.
• Undifferentiated – These cancer look completely different from normal cells anywhere in the body. Even with additional tests, it is often very difficult for a pathologist to determine where this type of tumour tumour started.
• Dedifferentiated – Dedifferentiated is used to describe a tumour that is made up of two different types of cancer cells. The first type of cancer cell looks similar to the previously normal cells. The second type of cancer cell looks very little or nothing like the normal cells. Dedifferentiated means that the less abnormal cells in the tumour have changed to become more abnormal and less like the original normal cells.

In most parts of the body, well and moderately differentiated cancers tend to grow more slowly and are less likely to spread to other parts of the body. In contrast, poorly differentiated and undifferentiated cancers are aggressive tumours that grow quickly and spread earlier to other parts of the body. Your doctors will use this information to help plan your care.