Persistence of disseminated tumor cells after radical prostatectomy: implications for tumor dormancy
Authors: Todd Morgan, Ilona Holcomb, Daniel Lin, William Ellis, Ian Gallaher, Marty Kinnunen, Bryce Lakely, Barbara Trask, Paul Lange, Robert Vessella
Journal: Cancer Research (2007)

AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA

5675 

Background: Men with apparently localized prostate cancer (PCa) often relapse years after radical prostatectomy (RP). In order to identify cells potentially responsible for this phenomenon, we isolated and characterized disseminated tumor cells (DTC) from the bone marrow (BM) of patients at the time of RP and in follow-up.

Methods: We obtained 895 BM aspirates from 790 patients with PCa at the time of RP and during follow-up. BM was also acquired from healthy men with PSA < 4.0 ng/ml as controls. We used density gradient centrifugation with Ficoll-Hypaque to obtain an enriched mononuclear cell population. This was followed by magnetic bead fractionation initially with antibodies to CD45 and CD61 (negative selection) and then with antibodies to human epithelial antigen (HEA; positive selection). The cells were stained with FITC-labeled anti-HEA antibodies (BerEp4), viewed under ultraviolet light, and isolated with a micropipette. Genomic DNA from these cells was amplified by ligation-mediated PCR and used for array comparative genomic hybridization (aCGH). The amplified material and a normal female reference were differentially labeled with fluorescent dyes and cohybridized to an array of BAC clones to detect relative copy-number loss and gain.

Results: DTC were detected in 74% (395/537) of patients prior to RP. There was no correlation with stage, Gleason grade, PSA, or tumor volume. Three of 25 controls (12%) had DTC present. Seventy percent (21/30) of patients with advanced disease had DTC in their BM aspirates. In patients post-RP and without evidence of disease (mean 4.2 years since RP, range 43 days to 18 years), DTC were present in 58/103 (56%). Only 6 of these 103 patients have recurred since the time of their BM aspirate and all had DTC present when they were still without evidence of disease. In pre-RP patients who underwent aCGH, all (n=54) had DTC with low-level changes. In comparison, all patients with metastases who underwent aCGH (n=6) had numerous, more pronounced genomic aberrations which included those commonly deviant in PCa, i.e. 8p loss and 8q gain. Furthermore, two of these patients had a high-level amplification on Xq that encompasses the androgen receptor.

Conclusions: Three-quarters of men undergoing RP had DTC detected in their BM prior to surgery, which is consistent with these cells escaping from the primary tumor early on in the disease. These early DTC had low-level copy-number changes, suggesting that they are tumor cells. In advanced stage patients the DTC had genetic changes which were more pronounced, implying an evolution in genomic aberrations. The high rate of detection of DTC in patients without evidence of disease (some >10 years) suggests that these are dormant tumor cells. What differentiates active DTC from dormant DTC is under investigation as are studies to determine the factor(s)/event(s) that trigger dormant DTC to become active.