Newer concepts of cancer of the colon and rectum: clinical evaluation of a radioimmunoassay for CEA

Problems of spectrum and bias in evaluating the efficacy of diagnostic tests

To determine why many diagnostic tests have proved to be valueless after optimistic introduction into medical practice, we reviewed a series of investigations and identified two major problems that can cause erroneous statistical results for the "sensitivity" and "specificity" indexes of diagnostic efficacy. Unless an appropriately broad spectrum is chosen for the diseased and nondiseased patients who comprise the study population, the diagnostic test may receive falsely high values for its "rule-in" and "rule-out" performances. Unless the interpretation of the test and the establishment of the true diagnosis are done independently, bias may falsely elevate the test's efficacy. Avoidance of these problems might have prevented the early optimism and subsequent disillusionment with the diagnostic value of two selected examples: the carcinoembryonic antigen and nitro-blue tetrazolium tests.

[Carcinofetal antigens. III. Further carcinofetal antigens (author's transl)]

The occurrance and significance of important carcinofetal antigens other than AFP and CEA are reported. These included the alpha 2 H-protein which is produced in the liver and increases in serum of patients with various tumors, the fetal sulphoglycoprotein antigen FSA from the gastric juice of patients with gastric cancer, the carcinoplacental alkaline phosphatase (REGAN-isoenzyme)which is found in the serum of patients suffering from e.g. bronchogenic, mammary, urogenital and gastrointestinal carcinomas, the beta-S-fetoprotein which is most likely to be identical with C-reactive protein, gamma-fetoprotein, the carcinofetal antigen in glial tumors (CFGA); ectopic production of placental hormones like human gonadotropin, placental lactogen, plasminogen-activators; leukemia-associated antigens. Furthermore, some other less known carcinofetal antigens are mentioned.

Carcinoembryonic antigen in patients suffering from ulcerative proctocolitis

Carcinoembryonic antigen (CEA) has been measured by radioimmunoassay in samples obtained from all patients suffering from ulcerative proctocolitis and seen within a four-month period. The characteristics of this group of patients have been compared with reported epidemiological studies in this disease, and have been found to have a similar sex ratio and age of onset, but a more limited disease. Among 59 patients, 11 were found to have elevated circulating CEA values. One of the 11 had a colonic carcinoma and another was pregnant. Excluding these two patients, an overall prevalence of elevated CEA levels of 17.5% was found. The prevelance in ulcerative proctitis was 7.1%, and in colitis was 19.9%. The patients in whom elelvated plasma CEA values were found were compared with the remaining patients in relation to factors known to be associated with an increased propensity for the development of colorectal carcinoma complicating ulcerative colitis. There was no difference in mean age of the patients at disease onset, nor was there any difference in disease duration, extent, and control. A significant correlation was found between elevated plasma CEA levels and the severity of the initial attack. One patient with premalignant changes in the rectal mucosa had consistently normal concentrations of plasma CEA. There was no significant correlation between elevated plasma CEA values and disease activity. The mean age of the two groups of patients was similar. No carcinoma has manifested in any patient during follow-up periods of at least 18 months.