Isolation and Characterization of Circulating Tumor Cells from Patients with Localized and Metastatic Prostate Cancer

Automated imaging of prostate-specific cancer cells from the blood provides a measure of circulating tumor cell half-life after tumor resection. Circling Cancers Out Oftentimes a patient and his or her clinician learn together at the flip of a radiological imaging scan that a solid tumor, previously removed, has returned either at the original site or at new locations to which it has spread. A failure of cancer treatment—but could it have been predicted? Whether it is freely floating tumor DNA or tumor cells, the circulation of cancer-derived material in the blood holds great promise for the early detection and prevention of cancer metastases. The accurate identification, enumeration, and molecular classification of blood-borne cells—although postulated more than 140 years ago—remain the greatest challenge. Now, in a small cohort of individuals with and without prostate cancer, Stott and colleagues have used a silicon microfluidic cell-capture technology that, when coupled to an automated imaging system, enables the detection and enumeration of prostate cancer cells fished out from the blood. These cells express a surface protein that uniquely identifies epithelial cells in the circulation. Once efficiently captured by antibody to this protein, the cells are counterstained with antibodies that are prostate-specific and that indicate cell proliferation, suggesting that these circulating cells are ready to repopulate distant metastatic sites. In their study, tumor cells obtained from the blood of cancer patients were monitored before and after surgery; some circulating cells persisted months after surgery while others rapidly declined shortly thereafter. Whether the persistence or disappearance of lurking cancer cells reflects an intrinsic capacity for reseeding remains to be established, but the system used in the study offers great potential for oncologists to detect cancer-related changes earlier and to monitor responses to drug treatments. In the hope of ultimately applying personalized treatments to cancer patients, based on “real-time” monitoring of the tumor cell genetic makeup, this approach to identifying these circulating cells early on moves us beyond the finality of the films currently offered to patients in the clinic. Rare circulating tumor cells (CTCs) are present in the blood of patients with metastatic epithelial cancers but have been difficult to measure routinely. We report a quantitative automated imaging system for analysis of prostate CTCs, taking advantage of prostate-specific antigen (PSA), a unique prostate tumor–associated marker. The specificity of PSA staining enabled optimization of criteria for baseline image intensity, morphometric measurements, and integration of multiple signals in a three-dimensional microfluidic device. In a pilot analysis, we detected CTCs in prostate cancer patients with localized disease, before surgical tumor removal in 8 of 19 (42%) patients (range, 38 to 222 CTCs per milliliter). For 6 of the 8 patients with preoperative CTCs, a precipitous postoperative decline (<24 hours) suggests a short half-life for CTCs in the blood circulation. Other patients had persistent CTCs for up to 3 months after prostate removal, suggesting early but transient disseminated tumor deposits. In patients with metastatic prostate cancer, CTCs were detected in 23 of 36 (64%) cases (range, 14 to 5000 CTCs per milliliter). In previously untreated patients followed longitudinally, the numbers of CTCs declined after the initiation of effective therapy. The prostate cancer–specific TMPRSS2-ERG fusion was detectable in RNA extracted from CTCs from 9 of 20 (45%) patients with metastatic disease, and dual staining of captured CTCs for PSA and the cell division marker Ki67 indicated a broad range for the proportion of proliferating cells among CTCs. This method for analysis of CTCs will facilitate the application of noninvasive tumor sampling to direct targeted therapies in advanced prostate cancer and warrants the initiation of long-term clinical studies to test the importance of CTCs in invasive localized disease.