Pathology dictionary -
Cancers start from cells that were previously normal and healthy. These normal cells can usually be found surrounding a tumour. Pathologists use the word differentiated to describe the difference between the cancer cells and the surrounding normal, health cells (non-cancerous) cells.
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 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 (non-cancerous) 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 outside of the tumour is call 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.
Why is this important? In most parts of the body, well and moderately differentiated cancers are associated with better prognosis compared to poorly differentiated and undifferentiated cancers. The prognosis for a dedifferentiated cancer is worse compared to cancers without areas of dedifferentiation.