Detection of micrometastasis by cytokeratin 20 RT-PCR is limited due to stable background transcription in granulocytes

The reverse transcription polymerase chain reaction (RT-PCR) amplification of cytokeratin 20 (CK20) mRNA is considered a promising candidate method fo r the detection of circulating tumour cells in bane marrow and peripheral b lood of cancer patients. In this study we have investigated the diagnostic specificity of the CK20 mRNA detection in samples from healthy donors (HD; n = 33), intensive care units patients (ICU; n = 20) and bone marrow obtain ed from patients suffering from chronic inflammatory diseases (CID; n = 14) . RNAs purified from stabilized lysates showed positive results in 24% of t he HD group (8/33), 35% of the ICU group (8/20) and in 40% of the CID group (5/14). The use of Ficoll gradients to separate nucleated cells completely restored the specificity of this CK20 RT-PCR assay. The CK20-expressing ce lls are positively identified to belong to the granulocyte fraction of leuc ocytes, which appear to express the gene on a background level. Our results demonstrate for the first time that CK20 mRNA expression is not limited to epithelium. its occurrence in normal granulocytes has to be considered in tests designed to detect circulating cancer cells or micrometastases. (C) 1 999 Cancer Research Campaign.