Table 1.

Tumor type and potential occult primary site

Tumor type	%	Potential occult primary (site/types)
Well or moderately differentiated adenocarcinomas	60	Lung, pancreas, hepatobiliary tree, kidney, colon, ovary, breast
Squamous-cell carcinomas	5	Head and neck, lung, cervix, penis, vulva, bladder
Carcinomas with neuroendocrine differentiation	1	Pancreas, GI tract, lung
Poorly differentiated carcinomas (including poorly differentiated adenocarcinomas)	25–30	Adenocarcinoma, melanoma, sarcoma, lymphoma
Undifferentiated neoplasm	5	Carcinoma, lymphoma, germ-cell tumors, melanoma, sarcoma, embryonal carcinoma