Tumor associated markers in clinical diagnosis.

Simple means for detecting the presence of tumors when they are still small and localized would be of major clinical benefit. Various tumor mark­ ers have been found and methods are available for measuring them in the blood. The results of studies suggest that the tumor markers of promise include onco-fetal antigens, placental antigens, polypeptide hormones and exocrine secretion products. Some, such as alpha-fetoprotein, are elevated early in the disease, frequently prior to detection by all other diagnostic aids. Others, notably carcinoembryonic antigen (CEA), are frequently only elevated when the tumor has progressed. The present-day practical appli­ cation of tumor markers is in monitoring the progression of the tumor and its response to therapy; under these conditions they are frequently more sensitive than other indices including scanning. Hum an chorionic gonado­ trophin has proved to be an excellent marker for following patients with trophoblastic neoplasms; its sensitivity as a marker can be improved by determ ining the levels of its alpha and beta subunits. The benefits of measuring ectopic hormone production including their precursors and par­ tial products require further study; in some instances a hormonal syndrome is the first clinical manifestation of the presence of malignancy. Certain markers, although not useful in aiding the diagnosis of cancers, may assist in predicting a response to specific therapy; these markers include the estrogen and progesterone receptors and lactalbumin. None of the known tumor markers w hen used alone have proved to be of sufficient value in population screening; nevertheless, when the levels are interpreted in con­ junction with other clinical and laboratory data, they frequently aid a diag­ nosis.