MEASUREMENT OF GLUTATHIONE-S-TRANSFERASE P1-1 IN PLASMA - PITFALLS AND SIGNIFICANCE OF SCREENING AND FOLLOW-UP OF PATIENTS WITH GASTROINTESTINAL CARCINOMA

BACKGROUND. Gastrointestinal tumors often contain high amounts of the detoxification enzyme glutathione S-transferase P1-1 (GSTP1-1). Elevat ed levels of GSTP1-1 were found in serum and plasma from most patients with gastrointestinal tumors. The authors evaluated the role of GSTP1 -1 as a plasma tumor marker in patients with gastrointestinal tumors. METHODS. A sensitive and specific sandwich enzyme-linked immunoadsorbe nt assay for quantification of GSTP1-1 in human plasma was developed. RESULTS, GSTP1-1 levels in serum samples from IO healthy controls were significantly (P < 0.0001) higher than in corresponding ethylenediami netetraacetic acid (EDTA) plasma and varied with the type of blood col lection tube used. Refrigeration or delayed centrifugation of blood co llected in plain EDTA tubes resulted in spuriously high plasma GSTP1-1 levels. Therefore, all plasma samples were collected in silicone-coat ed EDTA tubes. The distribution of plasma GSTP1-1 levels in 230 brood donors was nearly normalized by logarithmic transformation and an uppe r normal reference level of 21.8 mu g/L was calculated. Males had sign ificantly higher (P < 0.0001) plasma GSTP1-1 levels than females and a significant increase (P < 0.004) in plasma GSTP1-1 with age was noted . In only 20 of 55 patients (36%) with gastrointestinal tumors was the plasma GSTP1-1 level above the upper normal reference limit. No signi ficant decrease in plasma GSTP1-1 was noted in matched pairs of plasma samples collected from 17 patients before and at least 2 weeks after resection of the tumor. CONCLUSIONS. The GSTP1-1 level in serum and pl asma depends on the materials and methods used to collect the samples. Only 36% of the patients with gastrointestinal tumors had elevated pl asma GSTP1-1 levels that did not decrease after resection of the tumor . These findings argue against the use of GSTP1-1 as a serum or plasma marker for gastrointestinal tumors. (C) 1997 American Cancer Society.