Immunocytochemical patterns of islet cell tumors as defined by the monoclonal antibody HISL-19

A series of 51 islet cell tumors removed from 28 patients was investigated immunohistochemically with the monoclonal antibody HISL-19. The antibody was produced after immunization of BALB/c mice with human islet cells and was found to react with a wide range of neuroendocrine and neural cells. All tumors presented positive immunoreaction showing various combinations of 2 basic patterns. The first pattern reflected the immunostaining of the secretory granules of the tumor cells. This "granular" staining was predominantly associated with benign neoplasms and with the tumoral production of glucagon and pancreatic polypeptide (PP), while it was absent or inconsistent in most insulin-secreting tumors. The second pattern consisted of focal immunoreactive aggregates located in a peri- (and, in polarized cells, supra-) nuclear position. This "cluster-type" staining showed a good morphologic and topographic correspondence with the Golgi apparatus of the cells of the same tumors, as shown by electron microscopy. The latter pattern was well represented in all types of islet cell tumors except those producing PP. Moreover, it was more apparent in less differentiated tumors in which the granular pattern was often absent or inconsistent. Cluster-type (but not granular) immunoreactivity was frequently found in some nonendocrine, nontumoral pancreatic structures, particularly in the epithelium of small ducts. However, the immunoreactive aggregates of nonendocrine cells were distinctly less prominent than those of endocrine cells. On the basis of a comparison with other immunohistochemical markers for neuroendocrine cells, it is concluded that the HISL-19 monoclonal antibody presents specific staining characteristics useful for the cytologic analysis of islet cell tumors.