Carcinoid tumors are potentially malignant neoplasms that arise in various body sites, including the lung and gastrointestinal tract. Those that appear cytologically atypical are more likely to behave aggressively than more typical carcinoid tumors. However, in the absence of cytological atypia or large tumor size, it is difficult to predict the biology of an individual tumor, because some lesions metastasize, whereas others do not. The immunostaining reactions were quantitatively scored by three observers. All tumors stained with antibodies against synaptophysin.
Carcinoid tumors tend to have low proliferati- ve rates.
Immunostaining reactions with antibodies to NCAM, S-100, and chromogranin differ depending on the site of origin. In gastric adenocarcinoma the gastrin autocrine-paracrine pathway is activated. A high level of expression of precursor and mature gastrin peptides, together with the gastrin receptor, was seen in all carcinoids screened. In common with the glandular epithelium of the stomach the gastrin gene is activated during the neoplastic process in ECL cells. This finding may explain why some carcinoids do not regress after surgical procedures that lower serum gastrin.