Cytokeratin 20 is not a reliable molecular marker for occult breast cancercell detection in hematological tissues

Cytokeratins are potential markers for epithelial cell detection in hematol ogical tissues. Thus, we developed a nested reverse transcriptase-polymeras e chain reaction (RT-PCR) strategy to detect cytokeratin 20 (CK20) mRNA and studied its sensitivity and specificity as a molecular marker of occult br east cancer cells. In cell dilution experiments with human breast cancer ce ll lines, the limit of detection was 1 tumor cell in 1,000 hematological ce lls. In RNA dilution experiments of breast cancer cells' RNA in E. Coli tRN A, the CK20 transcript was only detectable when at least 1 ng of total tumo r RNA was present in a total of 1 mug of RNA mixture. In parallel experimen ts using colorectal cancer specimens, CK20 mRNA was detected with as little as 1 pg of total tumor RNA, suggesting a low level of CK20 mRNA expression in breast cancer cells. The CK20 transcript was detected in all six tumors and five hematological samples of breast cancer patients but in none of ni ne hematological cell lines. However, CK20 transcript was also detected in unfractionated nucleated cell population of hematological samples from 23 o f 31 (74%) healthy volunteers and from 12 of 24 (50%) patients with hematol ogical malignancies. When mononucleated and polymorphonucleated cell popula tions of hematological samples from these control groups were screened sepa rately, CK20 expression was detected in 94% of polymorphonucleated cell fra ctions and in 44% of mononucleated cell subpopulations. Thus, we conclude t hat the low sensitivity and specificity of RT-PCR detection of CK20 mRNA li mits its usefulness for breast cancer cell detection in hematological produ cts.