Biochemical markers of central nervous system tumors in cerebrospinal fluid.

Central nervous system (CNS) tumor markers that have been m easured in cerebrospinal fluid (CSF) include among others, lactate dehydrogenase (LDH), glutamic oxalacetic transaminase (GOT), aldolase, phosphohexose isomerase (PHI), lysozyme, creatinine kinase, isocitrate dehydrogenase, adenylate kinase, the polyamines and desmosterol. Such markers have at least five possible functions in the diagnosis and management of CNS neoplasms: screening, diagnosis, classification, early prediction of changes in clinical status and evaluation of efficacy of therapy. The predictive value model of Galen and Gam bino14 defines four parameters (sensitivity, specific­ ity, predictive value and efficiency) which can be used to determ ine the potential utility of each marker for each possible function. Since the low prevalence of CNS tumors (4.5 cases per 100,000 individu­ als) makes screening in the general population impractical, this model has been applied to the use of the aforementioned markers for diagnosis of CNS tumors in patients with neurological symptoms. The data from previous clinical studies have been collated and used to calculate the sensitivity and specificity of each marker. Very little data are available relative to the potential utility of these markers for the last three functions m entioned, except for desmosterol and polyamines. Finally, the possibility of a diagnos­ tic test for CNS tumors based on m easurem ent of more than one marker is proposed as a means of improving the low specificity of many of the markers studied.