Individualization of the cutoff value for serum squamous-cell carcinoma antigen using a sensitive enzyme immunoassay.

A sensitive enzyme immunoassay (IMx) for the squamous-cell carcinoma (SCC) antigen was used to evaluate low concentrations of this marker in the blood circulation. The assay can detect 0.05 ng/ml of serum SCC antigen, with intra- and interassay variabilities of 4.8 and 8.9%, respectively. Daily changes in serum SCC antigen were determined in healthy volunteers and in patients with cervical squamous-cell carcinoma after complete resection of the primary tumor, which revealed that, although the absolute values were variable from one case to another, the daily changes were relatively constant in each case, with a mean daily variation of 24.1 +/- 3.7% (mean +/- SE). The determination of the cutoff value for each individual patient may be effective for the early detection of an abnormal rise of circulating tumor marker, and will be useful in detecting small tumor foci during follow-up after treatment.