Acid phosphatase.

Acid phosphatase is a ubiquitous lysosomal enzyme that hydrolyses organic phosphates at an acid pH. Although the postpuberteral prostatic epithelial cell contains a uniquely high concentration of acid phosphatase, cellular components of bone, spleen, kidney, liver, intestine, and blood also contain this enzyme. The discovery that prostatic carcinoma cells often retain a high concentration of acid phosphatase characteristic of the normal postpubertal gland led to the recognition of the first clinically useful tumor marker. Recognition that the serum of patients with prostatic malignancy frequently contains an increased concentration of this enzyme has resulted in persistent efforts to identify the source, to accurately quantitate the level of serum acid phosphatase, and to determine the clinical significance of those levels. A variety of enzymatic and immunologic techniques have been employed to measure acid phosphatase. In the past, various substrates and inhibitors were utilized to increase specificity and sensitivity. Emphasis has now shifted to the development of radioimmunoassay and counterimmunoelectrophoresis in an attempt to enhance those parameters. Judgment of their efficacy awaits further testing and evaluation. The clinical significance of normal and abnormal serum acid phosphatase is constantly being reevaluated. In order to maximize the value of laboratory measurements, the clinical and pathologic status of the patient, the techniques employed in obtaining and storing the blood sample and the procedures used in analysis must be known and considered. Traditionally, the serum prostatic acid phosphatase has been thought to originate in the prostatic cancer cell and has been used to stage the disease. Until recently, elevated serum values have been accepted as an indication of extraprostatic disease, and were thought to rule out lesions confined to the prostate. The elevation of acid phosphatase levels in patients with disseminated disease or the failure of elevated levels to return to normal with treatment have been assumed to indicate a poor prognosis. However, unequivocal documentation of the validity of these statements is not available. Newer immunologic techniques for measuring acid phosphatase may significantly alter our current concept of its role as a tumor marker.