Beta-microseminoprotein in gastric carcinoids: a marker of tumour progression

Gastric carcinoid disease may have a highly varying clinical course depending on the malignancy of the tumour. Many biochemical markers, such as peptides and biogenic amines, have been found in carcinoid tumour tissue but none has been reported to be useful as a predictor of the degree of malignancy of the carcinoid. beta-Microseminoprotein is a small disulphide-rich protein with unknown function present in the secretions on most mucosal surfaces in the body, including the stomach where it is also found in some endocrine cells. We have studied beta-microseminoprotein by immunohistochemistry in the tumour tissue of 29 patients with gastric carcinoid disease. Beta-Microseminoprotein was present in the tumour tissue in 62% of the patients and its presence was correlated to tumour diameter and tissue invasion depth. The presence of beta-microseminoprotein in tumour tissue was corroborated by in situ hybridisation. All 4 patients with the solitary sporadic type of tumour and all 6 patients with metastasis had positive immunostaining of the tumour tissue. The serum concentration of beta-microseminoprotein, measured by radioimmunoassay, was increased in all but 2 of 13 patients with gastric carcinoid disease. To a large part the increase was due to the concomitant atrophic corpus gastritis. We conclude that beta-microseminoprotein in tumour tissue is a marker of tumour progression and that measurement of beta-microseminoprotein in serum is less informative than immunohistochemistry.