This study investigated the expression of placental glutathione S-transferase (GST-P) in late squamous cell carcinomas and its expression after withdrawal of short term carcinogen treatment using the hamster buccal pouch mucosa (HBPM) model, and compared the activity of GST-P with that of gamma-glutamyl transpeptidase (GGT). 25 of 32 (78%) tumors induced by an 18-week treatment with 0.5% dimethylbenz(a)anthracene (DMBA) stained positive with GST-P while only 2 (6%) tumors were positive for GGT. Numerous GST-P positive foci were present in the pouch epithelium with 3 weeks of DMBA treatment. At week 6, after 3-week discontinuation of the carcinogen treatment, the average number of GST-P foci was not significantly less than that of week 3. Numerous GST-P foci were still evident at week 9 after 6-week discontinuation of the carcinogen treatment, although the number was significantly less than those of weeks 3 and 6. In contrast, GGT foci were hardly identifiable after discontinuation of the carcinogen treatment and the number of GGT foci at both weeks 6 and 9 was significantly less than that of week 3. The results suggest that GST-P may be a more persistent and stable tumor marker than GGT in the HBPM model.

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