To the Editor: The presence of circulating tumor cells (CTC) in the peripheral blood of cancer patients has attracted a great deal of attention among investigators. The clinical significance of CTC has probably best been established in breast cancer, where it has been shown that the detection of CTC in metastatic patients correlates with early clinical relapse and patient death [1]. Gene expression profiling of CTC has been extended to other metastatic cancers including colorectal and prostate cancer [2,3].
Recently, a porous barrier density-gradient centrifugation system was developed that allows for enrichment of CTC from peripheral blood [4]. When coupled with the use of specific genes for real-time reverse transcriptase (RT)polymerase chain reaction (PCR), the buoyant density separation approach has the potential to increase sensitivity and specificity of CTC detection. We have previously utilized this system in combination with multi-marker real-time RT-PCR in a pilot study involving Stage IV breast cancer patients at the Medical University of South Carolina (MUSC). We detected breast cancerassociated overexpression in the peripheral blood of 13 out of 20 (65%) patients [5]. We also extended these observations to nonsmall cell lung cancer as 60% of patients with this tumor exhibited multimarker overexpression in their peripheral blood [6].
We enrolled 15 patients (11/15 of African-American ancestry) with advanced or metastatic AIPC in a clinical study sponsored by the General Clinical Research Center (GCRC) at the MUSC. The main objective of the study was to measure, by real-time, reverse transcriptase (RT)-polymerase chain reaction (PCR), the expression of a specific set of genes (EpCAM1, EpCAM2, XAG, S100P, DAG1, Claudin7, Ese1, Mal2, Spint2, ERG, and ETV1) in the peripheral blood of enrolled patients.
Results from 11 out of 15 enrolled patients could be analyzed and we found evidence of CTC in 8 of 11 subjects (6 of 8 for African-Americans). EpCAM1 and EpCAM2 were the most informative markers (Fig. 1). To the best of our knowledge, this is the first report identifying EpCAM2 as a marker for CTC in PCa, especially for African-American men.