Enzyme assays in malignant disease.

Although cancer diagnosis remains almost exclusively morphological, withhistological examination thelynch pin,there aresituations inwhichother techniques, suchasenzymeassays, mayprovide information ofclinical value. Itis,however, disappointing thatsomuchoftheincrease inknowledge ofthebiochemical properties oftumours has proved tobenonspecific, andtherefore oflimited diagnostic value.Nevertheless, tumourshave occasionally produced anunusual isoenzyme, an observation ofconsiderable biological anddiagnostic interest. Assaysofnormally occurring enzymesinserummay alsoyieldinformation of clinical valueincircumstances wherethelackof specificity isnotimportant; thus, whilst notindicatingthenature ofatumour, theymaynevertheless provide anindication ofitsactivity, ofitsresponse totreatment, orofthesite ofmetastases. Elevation ofserumenzymes bytumours maybe duetoleakage fromthetumourorfromadjacent normaltissue damagedbytheneoplasm. Serum enzymelevels mayalsobeinfluenced less directly, forexample whenthere isassociated haemolysis. Usually morethanoneofthese factors isoperative, asemphasized inthefollowing discussion. SerumAlkaline Phosphatase (EC3.1.3.1.) Assayofthis enzymecontinues tobeofgreat value inthedetection oflesions inliver andbone. Different isoenzymes havebeendemonstrated by various techniques inliver, bone,intestine, andplacenta. Somedegree ofdiscrimination ispossible onthe basis ofureainhibition, heatstability andelectrophoresis, therelative merits ofthelatter onvarious mediabeing discussed elsewhere inthis symposium byWiemeandDemeulenaere (p.51);however,