CUP syndrome

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Classification according to ICD-10
C80 Malignant neoplasm without specifying the location
- primary location unknown
ICD-10 online (WHO version 2019)

The acronym CUP for the English " c ancer of u Nknown p rimary " (shortened for: cancer of unknown primary origin ) has become established in the German-speaking countries and replaces the previously common term cancer of unknown primary tumor .


One speaks of a CUP if metastases are found without the malignant (malignant) primary tumor ( primary tumor ) being known. As a rule, these are histologically to neuroendocrine tumors such as small cell lung cancer , carcinoid tumors or malignant melanoma .

Prevalence and prognosis

The primary tumor is unknown in around 3–5% of all cancer patients. The prognosis is extremely unfavorable. Less than 25% of patients survive the first year after diagnosis.

Primary tumor search

In the case of CUP, there is histologically proven metastasis of an unknown primary tumor. The primary tumor search includes a dermatological examination of the entire skin, including the ear canal, nose, oral cavity and anus, as well as extensive sonography of all internal organs, endoscopy of the stomach, intestines and lungs, as well as examinations with high-resolution imaging procedures such as computed tomography and magnetic resonance tomography , in women also a gynecological examination and a mammography .


CUP usually develop when the primary tumor either goes away or remains very small. Since metastases are usually far more degenerate than the primary tumor, it is assumed that the immune system destroyed the tumor after metastasis or kept it small, whereas this was not possible with the highly malignant metastases. Another theory suggests that some of the CUP are caused by heterotopias , in which tissue was carried to other organs in the embryonic phase and degenerated there. In this case, the alleged metastases of a malignant melanoma in the lungs would in reality be a primary tumor.


Individual evidence

  1. N. Pavlidis, G. Pentheroudakis: Cancer of unknown primary site. In: The Lancet. 379, 2012, pp. 1428-1435, doi : 10.1016 / S0140-6736 (11) 61178-1 .
  2. JL Abbruzzese, MC Abbruzzese, KR Hess, MN Raber, R. Lenzi, P. Frost: Unknown primary carcinoma: natural history and prognostic factors in 657 consecutive patients. In: Journal of clinical oncology . Volume 12, Number 6, June 1994, pp. 1272-1280, ISSN  0732-183X . PMID 8201389 .