Prognostic factors in unknown primary cancer.

In patients with unknown primary cancer, the diagnostic uncertainty as to the nature of the primary cancer also affects the formulation of a prognosis. Only in a minority of patients, the similarity of the clinical presentations to those of known primary cancers at a similar stage has resulted in the identification of subsets of patients with favorable clinical and pathological features. Their recognition is of major importance since specific treatment guidelines may translate into prolonged survival. For the vast majority of patients with unknown primary cancer and unfavorable outcome features, the identification of reliable prognostic indicators has proven challenging. A number of studies with multivariate analyses identified poor performance status, liver metastases, and abnormal serum lactic dehydrogenase (LDH) levels as the main recurrent adverse prognostic factors. No international consensus has been defined. The knowledge of prognostic factors may help the oncologist to refine the daily management of patients, to assess the results of clinical trials, and to design more useful clinical research studies.