Cell types and cancer of unknown primary

Often when cells from a secondary cancer are examined, doctors can tell where they’ve spread from by their appearance and from tests done on the cells. For example, cells from a primary breast cancer that have spread to the liver will still look like breast cancer cells.

With CUP, doctors can’t tell what part of the body the cancer started in, but they may be able to find out the type of cell that’s changed. Knowing this can give your doctor more information about the possible primary cancer.

Most people with CUP have cancers known as carcinomas that come from epithelial cells. These cells line the inside or outside of a body organ. There are different types of epithelial cells, which can develop into different types of carcinomas. Adenocarcinomas and squamous cell cancers are the most common types to develop from these cells.

Adenocarcinomas develop from gland cells that line or cover certain organs in the body. About 70% of people with CUP have adenocarcinomas. The most common parts of the body for adenocarcinomas to start in are the breast|, colon|, prostate|, stomach|, pancreas|, womb| and lung|.

Squamous cell cancers develop from flat cells usually found on the surface of the skin or in the lining of internal surfaces of the body. About 5% of people with CUP have squamous cell cancers. These can start in the lung, skin|, head and neck| area, gullet (oesophagus)| and cervix|.

Sometimes carcinomas are classified as poorly differentiated. This means it’s not possible to tell what type of epithelial cell the cancer developed from.

A small number of people with CUP may have a type of cancer made up of specialised nerve cells that produce hormones, known as neuroendocrine cancers|.