The tube LAI assay measures accurately antitumor immunity in patients with early
cancer but fails to detect up to 75% of patients with advanced
cancer due to excess circulating
organ-specific neoantigen (OSN). Substances such as
prostaglandin E2 (
PGE2) or
aminophylline, which increase intracellular
nucleotides in leukocytes of patients with advanced
cancer reversed this nonreactivity and greatly increased the sensitivity of the assay without any loss of specificity. Antitumor immunity can now be detected in advanced
cancer, and a combination of the two assays gives prognostic potential to the assay: a positive test with
PGE2 and negative test without indicates the patient has a large
tumor burden. The specificity of the assay for each
cancer was high and in most instances was greater than or equal to 95%. The
PGE2 stimulated assay retained the high specificity. The sensitivity of the regular tube assay was often low, 33-56% because of the many advanced
cancer patients tested, whereas the
PGE2 stimulated assay showed almost a two-fold increase in sensitivity, 67-93%. The diagnostic value of the assay was estimated by calculating the predictive value for different prevalences of
cancer. It was found that at low prevalences of
cancer as found in the general population, the assay had a low diagnostic value since few patients with a positive test would have the
cancer tested for. With prevalences of
cancer of 5% or greater as might be found in a tertiary care clinical setting, the assay would seem to have diagnostic value since one half or more patients with a positive test would have the
cancer tested for. Most false positives, but not all, are found in patients who have lesions that are often considered to increase their risk for
cancer: severe dysplasia of the breast, colon
adenomas, chronic
atrophic gastritis and
chronic pancreatitis, suggesting that the assay predicts
oncogenesis.