Identification of carcinoma cells in peripheral blood samples of patients with advanced breast carcinoma using RT-PCR amplification of CK7 and MUC1.

We have undertaken a pilot study to attempt to identify circulating carcinoma cells in a series of patients with advanced breast carcinoma, using reverse transcription-polymerase chain reaction (RT-PCR) to amplify mRNA of epithelial specific antigens. Using this method to amplify mRNA of MUC1 and cytokeratin 7 (CK7) the sensitivity of the technique was demonstrated by means of diluted concentrations of "spiked MCF7" cells in whole blood, showing a detection limit of 1 in 10(6) (CK7) and 1 in 10(5) (MUC1). Positive results were obtained from the peripheral blood of all nine female patients with advanced breast cancer for CK7 and eight of the nine patients for MUC1. CK7 was however detected in five of 11 healthy controls (eight females, three males) and MUC1 in one of the 11 controls. None of the control group were positive for both CK7 and MUC1, in contrast to eight of the nine patients with advanced breast carcinoma who were positive for both markers. The RT-PCR method thus appears sufficiently sensitive to identify circulating tumour cells in peripheral blood samples from patients with advanced breast carcinoma. However a high proportion of false-positive results was seen in the control population. More extensive investigation is required before the technique is likely to be of benefit clinically.