Cytoplasmic leucine naphthylamidase activity expressed in signet-ring cell carcinoma of the stomach.

Histochemical studies were performed on signet-ring cells in surgically resected gastric carcinomas from 64 patients. On the basis of periodic acid-Schiff reactivity of the intracellular mucin, the signet-ring cells were classified as type A (immature), type B (intermediate), or type C (mature). Different staining reactions to Alcian blue at pH 2.5 enabled type C cells to be subclassified as C-1 or C-2. In 63 cases (98.4%), intense leucine naphthylamidase (LNAase) activity was found histochemically in the cytoplasm of nearly all cancer cells except type C-2. Localization of LNAase activity in the cytoplasm was confirmed by conventional biochemical assay. From the present results, histochemical characteristics of signet-ring cell carcinoma are discussed.