CK20 gene expression: Technical limits for the detection of circulating tumor cells

The suitability of CK20 mRNA expression as a marker for the defection of mi nimum residual disease in patients with cancer of epithelial origin was eva luated. A sensitive nested RT-PCR assay with multiple replicates was optimi sed to detect a minimum number of circulating tumor cells expressing cytoke ratin 20 (CK20) mRNA. Using this optimal procedure, we examined CK20 mRNA e xpression in ten epithelial and seven leukemic cell lines, in eight bladder tumors, in peripheral blood samples from 18 tumor patients and from 29 hea lthy controls and in 8 bone marrow samples from healthy donors. CK20 mRNA w as found in 13 of 18 (72%) blood samples from patients with cancer of epith elial origin and in all the epithelial tumor cells tested. However, CK20 mR NA was also detected in 21 of 29 (72%) bloods, in 8 of 8 bone marrow sample s from healthy donors and in 4 of 7 leukemic cell lines. These results high light a requirement for either determination of threshold levels of CK20 no rmal expression or the development of quantitative techniques to distinguis h between a tumor-specific CK20 gene expression and a low level background transcription of this marker. These results would also advise caution in us ing CK20 as a tumor specific marker in clinical investigations.