Detection of MUC1-expressing mammary carcinoma cells in the peripheral blood of breast cancer patients by real-time polymerase chain reaction.

We have prospectively analyzed blood samples of 122 patients with breast disease for the presence of circulating expressing MUC1 cells before and after treatment. Among them, 28 patients had histologically confirmed benign breast disease (group 1), 34 patients had operable breast cancer (group 2), and 60 patients had advanced breast cancer (group 3). Circulating epithelial cells were isolated with BerEP4-coated immunomagnetic beads. Total RNA was extracted and reverse transcribed before analysis by real-time PCR of a MUC1-specific cDNA sequence. The sensitivity of the reverse transcription-PCR tested with blood spiked with MCF7 cells was one cell in 5 ml of blood. The immunomagnetic separation step was mandatory to obtain the maximum specificity. Control samples from healthy donors never displayed cycle threshold (Ct) values for MUC1 lower than 38. Circulating cells (Ct, <38) were detected in 3 of 28 (11%) cases in group 1, in 8 of 34 (24%) cases in group 2, and in 27 of 60 cases (45%) in group 3. A semiquantitative estimate of blood-borne cells could be derived from the Ct value when below 32 (the lowest was 28) or by the number of positive aliquots of the same blood sample. Thus, immunomagnetic separation, followed by MUC1-specific RT-PCR, allows the semiquantitative detection of circulating mammary cells. A significant correlation between the presence of MUC1-positive cells and the group of breast tumors was observed. The clinical significance of blood-borne cells in breast cancer, especially at the operable stage, may be investigated by following these patients.