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Poorly differentiated cancer from an unknown primary site

John D Hainsworth, MD
F Anthony Greco, MD
Section Editor
George P Canellos, MD
Deputy Editor
Sadhna R Vora, MD


Cancer of unknown primary site (CUP) is a relatively common clinical entity, accounting for approximately 4 to 5 percent of all invasive cancer diagnoses [1]. Within this category, tumors from many primary sites with varying biology are represented. Most cancers of unknown primary site are adenocarcinomas and can be recognized by routine histologic examination. However, 20 to 25 percent of CUPs are poorly differentiated and cannot be precisely characterized by histologic examination. About 80 percent of these poorly differentiated tumors have features of carcinoma, and are termed “poorly differentiated carcinoma” after initial pathologic examination. In the remainder, histologic examination results in the diagnosis of “poorly differentiated neoplasm,” signifying the inability to distinguish between carcinoma, melanoma, lymphoma, sarcoma, or germ cell tumor.

As accurate a diagnosis as possible is essential since the therapy for various tumors can be quite different and may be curative in some patients. The diagnostic approach to poorly differentiated cancers of unknown primary site will be reviewed here, along with the prognostic and therapeutic implications.

Other relevant topics include:

(See "Overview of the classification and management of cancers of unknown primary site".)

(See "Adenocarcinoma of unknown primary site".)

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Literature review current through: Nov 2017. | This topic last updated: Mar 03, 2017.
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