by Jason Wasserman MD PhD FRCPC
March 9, 2022

What does undifferentiated mean?

Pathologists use the word undifferentiated to describe a tumour made up of cells that do not look anything like the normal, non-cancerous cells found in the area of the body where the tumour started. Because undifferentiated cancer cells are so abnormal-looking when examined under the microscope, your pathologist may not be able to determine the specific tumour type or exactly where the tumour started.

Undifferentiated tumours are often aggressive tumours that quickly spread to other parts of the body such as lymph nodes, lungs, liver, and bones. The movement of tumour cells to another part of the body is called metastasis.


Why are the levels of differentiation?

Undifferentiated is on one end of a scale that pathologists call differentiation. This scale is used to compare cancer cells to normal cells. In most areas of the body, the scale includes 4 levels of differentiation.

  • Well-differentiated – These tumour cells look very similar to normal, healthy cells but they still behave in a manner that makes them a cancer.
  • Moderately differentiated – These tumour cells are abnormal-looking but still share some features with normal, healthy cells.
  • Poorly differentiated – These tumours cells look very little like normal, healthy cells.
  • Undifferentiated – These tumour cells look and behave nothing like normal, healthy cells.

What other tests may be performed when examining undifferentiated cells?

Your pathologist may order additional tests, such as immunohistochemistry or next-generation sequencing (NGS) to better understand an undifferentiated cancer and to try to determine where the cancer started.

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