CUP is represented by a heterogeneous group of diseases all of which have presented with metastasis as the primary manifestation. Although the majority of diseases are relatively refractory to systemic treatments, there are certain clinical presentations of CUP that carry a much better prognosis. In each instance, there are distinct clinical and pathologic details that require consideration for appropriate, potentially curative, management. Adrenal involvement has also been noted to be a poor prognostic finding. Lung metastases are twice as common in primary sites ultimately found to be above the diaphragm.
Liver metastases are more common from primary disease below the diaphragm.
The pattern of metastasis from a carcinoma presenting as CUP may be significantly different from that which would be expected from the usual presentation. For instance, bone metastases are approximately 3 times more common in pancreatic cancer presenting as CUP, while osseous metastasis from lung cancer is about 10 times less common when it presents as CUP compared with the usual presentation. The biologic bases for these differences in presentation, incidence, and pattern of metastases are unknown. Cancer incidence in New South Wales, Australia. Treatment of the patient with adenocarcinoma of unknown origin.