A primary approach to cancers of unknown primary

Schwartz and Harpaz talk about cancers of unknown primary organ (CUP), which is defined as metastatic cancers whose anatomic origin is clinically not detectable even after a thorough diagnostic evaluation. The pathologic diagnoses of CUPs in metastatic sites tend to he carcinomas, of which the majority are adenocarcinomas. The initial diagnostic approach seeks to exclude atypical but benign reactive process and then classify the malignancy as a carcinoma or other malignancies such as sarcomas, lymphomas, and melanomas. An immunohistochemical (IHC) panel can separate the majority of these tumor types. Histopathologic features combined with histochemical mucin stains usually permit distinction between adenocarcinomas and other cancers, namely, squamous cell carcinomas, poorly differentiated carcinomas, germ cell cancers, neuroendocrine carcinomas, and the occasional mesotheliomas that mimic a sarcoma or adenocarcinoma.