The management of patients with adenocarcinoma and poorly differentiated carcinoma of unknown primary site.

Patients with metastatic carcinoma of unknown primary site form a heterogeneous group, and optimal management of these patients requires the recognition and identification of treatable subsets within this large group. A large percentage of these patients have well-differentiated adenocarcinomas of unknown primary site. Although many of these patients currently have unresponsive neoplasms and short survival expectations, certain identifiable subsets respond well to systemic therapy, with prolongation of survival and, in some cases, cure of their malignancies. Patients with poorly differentiated carcinoma or poorly differentiated adenocarcinoma of unknown primary site make up a substantial minority of all these patients and require careful evaluation. Specialized pathologic evaluation, including immunoperoxidase staining and electron microscopy, is often helpful in diagnosis. Careful clinical evaluation, including staging with chest and abdominal computed tomography scans, and measurement of serum human chorionic gonadotrophin and alpha-fetoprotein, is also important. In some patients, no diagnosis more specific than "poorly differentiated carcinoma" can be made; these patients often respond well to cisplatin-based chemotherapy, particularly if the tumor is located in the mediastinum, retroperitoneum, or lymph nodes. Another responsive subset of patients are those with neuroendocrine differentiation identified either by electron microscopy or immunoperoxidase staining. These patients also respond to systemic chemotherapy, and some have the opportunity for long-term survival.