Heterogeneity in alkaline phosphatase isozyme expression in human testicular germ cell tumours: An enzyme-/immunohistochemical and molecular analysis

In humans, alkaline phosphatases are encoded by one tissue-non-specific alk aline phosphatase (TNAP) gene and three tissue-specific alkaline phosphatas e genes, intestinal, placental (PLAP), and germ cell-specific alkaline phos phatase (GCAP). Although the presence of alkaline phosphatases in testicula r germ cell tumours (TGCTs) of adolescents and adults has been utilized for both detection and patient monitoring, it is not known in detail which iso zymes are expressed. Since alkaline phosphatase is detected in carcinoma in situ (CIS), the common precursor of all TGCTs, it might provide a marker f or the early diagnosis of TGCTs. Testicular cancers of germ cell and non-ge rm cell origin along with testicular parenchyma with and,without CIS have b een analysed for the expression of the different alkaline phosphatase isozy mes. Antibodies to TNAP and PLAP/GCAP showed positivity in CIS, seminoma, a nd embryonal carcinoma. The heterogeneous staining pattern detected in froz en tissue sections was similar to the pattern found in formalin-fixed, para ffin-embedded material, indicating a biological phenomenon and not a handli ng artefact. Since PLAP and GCAP cannot be distinguished using immunohistoc hemistry, the expression of these isozymes was studied at the molecular lev el using a reverse transcriptase-polymerase chain reaction (RT-PCR) approac h, in combination with a primer extension assay, The results show that CIS and seminoma predominantly express GCAP, while in embryonal carcinoma the e xpression of GCAP versus FLAP varies. Due to the presence of alkaline phosp hatase transcripts in normal testicular parenchyma, an RT-PCR-based analysi s of alkaline phosphatase is not informative for the early detection of TGC Ts in biopsy samples. Copyright (C) 1999 John Wiley & Sons, Ltd.