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Cancer of unknown primary site

For cancer in which the primary site is unknown, metastasis exists but the primary tumor is not identified after performing a thorough medical work-up.

    In Norway, the term origo incerta is often used instead of "cancer of unknown primary site." In the literature, it is common to use the abbreviation, CUP (metastatic cancer of unknown primary site).

    CUP constitutes 3–5% of all malignant cancers and <1 % of pediatric cancers.

    The incidence of metastatic cancer of unknown primary site has reduced significantly over recent years. In 2010, The Cancer Registry of Norway reported only about 1.5% of all malignant diseases with this classification. CUP constitutes <1% of pediatric cancers.

    The patient group is heterogeneous and there are large variations in disease profiles and tumor histology (1). In an unpublished Norwegian study by Gundersen et al, the most common localizations for metastases are (4):

    • lymph nodes (36%)
    • abdomen (20%)
    • lungs/pleura (9%)
    • central nervous system (8%)

    Studies have shown that autopsy can reveal CUP in three out of five patients. The most common origins are lung (27%), pancreas (24%), liver/bile duct (8%), kidney or adrenal gland (8%), large intestine and rectum (7%), sex organs (7%) and stomach (6%) (2).

    CUP can lead to an increased psychological burden compared to other cancer diagnoses due to the extent of time and unanswered questions, as well the less specific treatment compared to a diagnosis of known origin. Extra awareness should therefore be paid to the increase in psychological stress this uncertainty causes and coupled with good supportive care. 


    In Norway, the incidence was reduced from 770 patients in 2000, to 484 patients in 2015. Less men than women receive this diagnosis (219 compared to 265, respectively in 2015).

    The median age is 60 years.


    Age-specific incidence of cancer of unknown primary site, 2009–2013.

    Source: Cancer Registry of Norway



    Incidence of cancer of unknown primary site, 1954–2013.

    Source: Cancer Registry of Norway


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