Immunohistochemistry of eccrine poroma and porocarcinoma--more than acrosyringeal tumors?

Sweat gland tumors have been classified according to their presumed physiological counterpart of the sweat apparatus. Both benign poroma and malignant porocarcinoma are thought to be acrosyringeal tumors. In order to specify this general assumption, we performed histochemistry and immunohistochemistry on paraffin sections of 29 poromas and eight porocarcinomas. In detail, we used Lapham's stain, Masson's silver impregnation, and immunoperoxidase staining with glandular marker antibodies against glycoproteins (CEA, LS59, NKI/C-3) and intermediate filament proteins (wide spectrum keratin, Cam 5.2, Vim 9(1)). Poromas disclosed some scattered S100-positive dendritic cells, red-stained cells in Lapham's method, several silver impregnated dendritic cells, and numerous cells surrounding poromas which were positive for LS59 and NKI/C-3. The labeling with wide spectrum keratin antiserum was low compared to epidermal keratinocytes. Porocarcinomas made some difference. CEA-positive single vacuolated cells could be observed, and S100-positive cells failed to show dendrites as in poromas. Some tumor cell clusters were stained weakly with LS59 and NKI/C-3 in addition to surrounding cells in both tumor entities. Three out of eight porocarcinomas disclosed sparsely distributed scattered cells weakly reactive with antibodies Cam 5.2 or Vim 9(1). In general, malignant porocarcinomas expressed a greater variety of cellular markers than benign poromas. The differentiation of both tumors, however, was directed toward inner duct cells and myoepithelium. Since myoepithelial cells are missing in normal acrosyringium, poromas and porocarcinomas are thought to be sweat gland tumors related to the distal portion of the dermal duct.