Hello and thanks for posting a question on the forum

Cancer is usually diagnosed through the looking at and testing of a biopsy or tissue sample that usually reveal where the cancer originated according to the cell type.

Cancers in time can also spread to other organs of the body and if found these are known as secondary cancers that have spread from the primary cancer site.

However there are instances where the cells reveal such a mixed picture of cells it is difficult to know where the cancer started and these are often called a cancer of unknown primary (CUP). Often when this happens the doctors will try very hard to work out where the cancer started so they can give the best treatment/s possible but this isn't always possible even when a variety of different tests and scans are carried out.

You can read more about CUP here.

I hope this is useful but do get back if you have further questions. We also have a telephone helpline that operates Monday-Friday 9-5 and you are welcome to contact us this way if you prefer.

Best wishes

Naomi