Overview

Carcinoma of unknown primary is a diagnosis given when doctors aren't able to locate where a cancer began.

Most often, cancer is diagnosed when doctors discover the spot where the cancer began (primary tumor). If the cancer has spread (metastasized), those sites might be discovered, too.

In carcinoma of unknown primary, also known as occult primary cancer, doctors find the cancer cells that spread in the body, but they can't find the primary tumor.

Doctors consider the location of the primary tumor when choosing the most appropriate treatments. So if carcinoma of unknown primary is found, doctors work to try to identify the primary tumor site. Your doctor might consider your risk factors, symptoms, and results from exams, imaging tests and pathology tests when trying to determine where your cancer began.