Measurement of glutathione S-transferase pi isoenzyme in plasma, a possible marker for adenocarcinoma of the lung.

Using a specific radioimmunoassay, we measured glutathione S-transferase (GST; EC 2.5.1.18) pi isoenzyme in the plasma of 29 patients diagnosed as having carcinoma of the bronchus. Concentrations of the enzyme were significantly higher (P less than 0.01) than those measured in a control group of 16 patients with respiratory disorders other than malignancy. Although, overall, only 19 (66%) of patients with cancer of the bronchus had increased concentrations of GST pi in plasma, eight of the nine (89%) patients diagnosed as having adenocarcinoma had above-normal concentrations of GST pi. To obviate spuriously high results for GST pi concentrations caused by platelet release, we assayed blood samples collected in "Thrombotect" tubes, which contain inhibitors of platelet activation.