Canadian Cancer Society logo

Cancer of unknown primary

You are here: 

Grades of cancer of unknown primary

Grading is a way of classifying cancer of unknown primary (CUP) cells based on their appearance and behaviour when viewed under a microscope. To find out the grade of a tumour, the biopsy sample is examined under a microscope. A grade is given based on how the cancer cells look and behave compared with normal cells (differentiation).

With cancer of unknown primary (CUP), the doctor (pathologist) will try to identify the type of cell the cancer developed from (histology). The most frequently occurring CUPs are:

  • adenocarcinomas
    • Adenocarcinoma CUP may be well or moderately differentiated. Well or moderately differentiated means the cancer cells look and behave similarly to normal cells.
    • Only some adenocarcinomas are poorly differentiated.
  • undifferentiated or poorly differentiated cancers
    • Undifferentiated or poorly differentiated means the cancer cells look and behave quite differently from normal cells.
    • These cells do not look like any particular type of body cell (like a breast or prostate cell) because they are too primitive (immature). This can make it difficult for the doctor to know exactly where the cancer started.

Identifying the cell type plays an important part in planning treatment for CUP. It can also be used to help judge a person's prognosis (future outcome).


Kim Moreau Help Whip Cancer has made such a difference in the lives of so many women.

Read Kim's story

A helping hand for families

Illustration of crowd

The Canadian Cancer Society helps with expenses for children in cancer treatment and their families.

Learn more