Expression of human prostatic acid phosphatase in a pancreatic islet cell carcinoma

The immunologic specificity of human prostatic acidphosphatase has been established by several previous investigations as well as in this study. An apparent exception to this specificity was observed--a case of pancreatic islet cell carcinoma metastasized to the liver produced acid phosphatase that was immunologically indistinguishable from the prostatic acid phosphatase. In this case, the possibility of prostatic involvement was convincingly ruled out by clinical follow-ups and by postmortem pathologic studies. Highly purified prostatic acid phosphatase and this tumor acid phosphatase exhibited very similar Km values and identical molecular weights. Immunochemical analysis of the two enzymes using antiprostatic acid phosphatase sera showed that enzymes are antigenically identical. The implications of our observation are discussed in relation to clinical application of immunoassays for prostatic phosphatase in the future and to the molecular basis of human acid phosphatase polymorphism.