The Histochemical Journal 32: 551–556, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Detection of chromogranin A in human gastric adenocarcinomas using a sensitive immunohistochemical technique Gunnar Qvigstad 1,2 , Arne K. Sandvik 1 , Eiliv Brenna 2 , Steinar Aase 3,∗∗ & Helge L. Waldum 2,∗ 1 Department of Physiology and Biomedical Engineering, 2 Department of Intra-Abdominal Diseases, 3 Department of Laboratory Medicine, Norwegian University of Science and Technology, University Hospital, N-7006 Trondheim, Norway ∗∗ Present address: Department of Pathology, Telemark Central Hospital, Norway, Department of Pathology, Faculty of Dentistry, University of Oslo, Norway ∗ Author for correspondence Received 16 May 2000 and in revised form 25 July 2000 Summary Neuroendocrine cells are often disclosed in human gastric adenocarcinomas and may be recognised by their immunoreactivity towards chromogranin A. However, in dedifferentiated neuroendocrine tumour cells, the chromogranin A content may be reduced making it difficult to detect with conventional immunohistochemical methods. We therefore used a sensitive signal amplification technique in order to evaluate chromogranin A immunoreactivity and thus neuroendocrine differentiation in 40 gastric adenocarcinomas. Neuroendocrine cells were visualised by means of a monoclonal chromogranin A antibody and the avidin–biotin peroxi- dase complex technique, without and with addition of tyramide signal amplification. Double immunohistochemistry towards chromogranin A and Ki-67 were used to disclose proliferation in the neoplastic cells. A marked increase in the number of carcinomas containing chromogranin A-immunoreactive neoplastic cells was noted when applying the tyramide signal amplification technique. In addition, the number of immunoreactive cells within each tumour increased, and in some cases almost all the neoplastic cells became immunoreactive. Chromogranin A-immunoreactive tumour cells showing signs of proliferation were found in the majority of these carcinomas. In conclusion, we have disclosed widespread immunoreactivity towards chromogranin A in a proportion of gastric adeno- carcinomas when enhancing the signal with tyramide signal amplification. Neuroendocrine differentiation is thus a common finding in gastric carcinomas when using sensitive methods. Introduction Neuroendocrine cells are found in most epithelial surfaces of the body and are known to have important regulatory functions. Like many other cells, the neuroendocrine cells may undergo neoplastic transformation and are the origin of such classical neuroendocrine tumours as the carcinoids and small (oat) cell lung carcinomas (SCLC). Cells that show immunoreactivity for neuroendocrine markers have also been found in adenocarcinomas from several organs, such as the lung (Linnoila et al. 1988) and stomach (Waldum et al. 1991), but the significance of these cells is not settled. The prevail- ing view has been that these cells represent terminal neuroen- docrine differentiation of tumour cells without the capacity for further proliferation (Ooi et al. 1992). Neuroendocrine cells contain secretory granules which may be detected in tissue sections by immunohistochemistry using antibodies towards chromogranin A (CgA) (Wilson & Lloyd 1984). Even in carcinoids and SCLC, only a proportion of the neoplastic neuroendocrine cells show CgA immunore- activity when using conventional immunohistochemical techniques (Sumiyoshi et al. 1998, Qvigstad et al. 1999). Dur- ing neoplastic transformation and progression, specific cell markers like secretory granules can become reduced in num- ber or even completely lost (Creutzfeldt et al. 1973, Gould et al. 1983). Conventional immunohistochemical techniques used to visualise specific antigens in these granules may, therefore, show a false negative reaction in such dedifferen- tiated tumour cells (Deftos et al. 1988, Qvigstad et al. 1999). Amplification of immunohistochemical and in situ hybridi- sation signals may be achieved by catalytic deposition of biotinylated tyramide on the tissue sections (Adams 1992). This tyramide signal amplification (TSA) technique has been shown to increase the sensitivity considerably (Merz et al. 1995, Wiedorn et al. 1999). Since neuroendocrine cells are often detected in gastric carcinomas, we found it of interest to re-examine our previously published series of such tumours (Waldum et al. 1998), utilising the sensitive TSA method. In our previous report, we found signs of neuroendocrine mark- ers in a substantial number of the carcinomas, but often the neuroendocrine cells were few. To elucidate the possible sig- nificance of such neuroendocrine cells in gastric carcinomas,