What is cancer of unknown primary (CUP)?

Cancer cells are abnormal malignant cells that grow and multiply in an uncontrolled manner. They can form a mass, known as a tumor. In some cases, cancer cells leave this initial tumor—called the primary tumor—spread to other parts of the body, and form secondary tumors known as metastases.

Cancer of unknown primary (CUP) is a cancer diagnosed through the presence of metastases for which the primary tumor cannot be identified. It is also referred to as occult primary cancer or cancer of unknown origin. Each year, nearly 7,000 new cases of cancer of unknown primary are diagnosed in France¹.

This is a complex medical situation, as identifying the nature and tissue of origin of the initial cancer cells is essential in order to select the most appropriate treatment. In recent years, the use of advanced technologies has improved the ability to identify the origin of metastases in cancers of unknown primary, making it possible to offer more personalized treatments. This approach requires specific expertise, which is available at Institut Curie, which also coordinates the national multidisciplinary consultation meeting dedicated to cancers of unknown primary.

¹ Rassy E, Pavlidis N. The currently declining incidence of cancers of unknown primary origin. Cancer Epidemiol 2019; 61: 139-141.