Diagnostic significance of levamisole-resistant alkaline phosphatase in cytochemistry and immunocytochemistry

The authors have used two immunoalkaline phosphatase methods to study nonhematopoietic tumor tissues of four patients, one each with alveolar cell carcinoma of the lung, renal cell carcinoma, gastric adenocarcinoma, and colon carcinoma. They found, regardless of specific antibodies used, definite enzyme activity in the tumor cells of these four patients. Although it was possible to determine that the tumor cells were epithelial in origin because of their intense staining with antibodies to epithelial cell antigens, control slides labeled with nonimmune mouse ascites also contained cells with definite enzyme activity. In two of these cases, unlabeled smears were stained for alkaline phosphatase and showed that the tumor cells contained endogenous levamisole-resistant enzyme activity. This endogenous enzyme activity is not demonstrable in either the benign cells of these cases or the benign or malignant cells of other control cases. The findings suggest that the immunoalkaline phosphatase methods also have their inherent endogenous enzymic problems. They also suggest that cytochemical demonstration of levamisole-resistant alkaline phosphatase may be a useful cell marker for the identification of tumor cells in serous effusions.