Quantitative polymerase chain reaction for the detection of micrometastases in patients with breast cancer

Purpose: Previous reports have indicated that reverse transcriptase polymer ase chain reaction (RI-PCR) for cytokeratin 19 (CK-19) may be useful in the management of patients with breast cancer, However, the specificity of thi s technique is low, principally because of a high rate of false-positive re sults, To improve the specificity of this assay we developed a quantitative RT-PCR methodology that enables an estimate to be made of the number of CK -19 transcripts in blood and bone marrow samples, Patients and Methods: We examined 45 peripheral blood samples and 30 bone m arrow samples from patients with a variety of nonneoplastic conditions usin g nested RT-PCR for CK-19, We also examined bone marrow and peripheral-bloo d samples from 23 patients with primary breast cancer and peripheral-blood samples from 37 patients with metastatic breast cancer. The number of CK-19 transcripts was estimated in positive specimens by competitive PCR and nor malized to the number of ABL transcripts as an internal control for the qua lity and quantity of cDNA, RT-PCR results were compared with the numbers of CK-19-positive cells detected by immunocytochemistry, Results: Analysis of samples from patients without cancer enabled us to def ine an upper limit for the background ratio of CK-19 to ABL transcripts (1: 1,000 for blood samples and 1:1,600 for bone marrow samples). Using these f igures as cut-off points, elevated CK-19: ABL ratios were detected in perip heral-blood samples of 20 of 37 (54%) patients with metastatic breast cance r and in bone marrow samples of 14 of 23 (61%) patients with primary breast cancer. Only three of 23 (13%) primary breast cancer peripheral-blood samp les and none of the control samples were positive by these criteria, Only t wo of 23 patients (9%) with primary breast cancer showed immunocytochemical ly detectable cells in the blood; 10 of 23 (43%) showed immunocytochemicall y detectable cells in the bone marrow,Of 36 patients with metastatic breast cancer, eight (22%) showed positive events. Conclusion: Quantitative RT-PCR for CK-19 detects a percentage of patients with breast cancer and may enable the progression or regression of the dise ase to be monitored. (C) 1999 by American Society of Clinical Oncology.