Release of tumor cells into the circulation during prostatic surgery: We recruited 103 men undergoing prostate removal surgery for early-stage prostate cancer. We drew blood from both the vessels draining the prostate gland and from an arm vein, collecting samples during and immediately after surgery. Interestingly, most patients had hundreds of prostate‐derived cells in the tumor-draining blood. Patients with high PSA levels before surgery were more likely to have CTCs in peripheral blood, suggesting a connection between tumor burden and the likelihood of finding cancer cells in circulation. Longer patient follow-up observations and larger trials will be essential to determine whether perioperative strategies to reduce tumor cell release can translate into better long-term outcomes for men with prostate cancer.
Release of tumor cells during breast tissue biopsy and surgery: In our study of 206 women undergoing needle or core biopsies for suspected breast lesions, we drew blood samples immediately before and after their biopsy. Of the 118 women whose biopsies confirmed cancer, 17% showed a rise in CTC number after biopsy. This increase in CTCs occurred more often in patients whose tumors lacked E-cadherin, a molecule that helps cells stick together, suggesting that tumors already prone to loosen their cell-to-cell bonds are especially likely to shed cells when disturbed (Figure 1).
In addition to the CTCs, we collected and isolated cell-free DNA from the blood plasma from women that underwent tissue biopsy. We next assessed the methylation status of a large panel of oncology related genes to identify the tumor specific DNA among the normal DNA. With this, we aim to reduce the number of invasive tissue biopsies to women with the highest likelihood of having breast cancer. Namely, from the 206 women we recruited, 43% had no malignant disease and were thus over diagnosed. This highlights the urgent need for more precise and less intrusive diagnostic tools.
Peripheral blood samples were analyzed before and shortly after breast cancer surgery from 52 breast cancer patients. Preoperatively, CTCs were detected less frequently than post-surgery (5.8 vs 13.5%). The clinical follow-up data of the patients examined in this study are currently being evaluated and will then be compared with the results of the CTC analyses.
Molecular CTC characterization: To confirm the malignant identity of CTCs detected in the above studies, we obtained 26 cells and performed whole-genome sequencing. Of the 19 cells extracted from the prostatic plexus, 10 were identified as tumor cells and 9 as normal epithelial cells; of the 7 cells from the peripheral blood, 4 were identified as tumor cells and 3 as normal epithelial cells.
Functional studies: From the CTCs of a breast cancer patient, we established a permanent cell line that we used to study tumor cell extravasation. With it, we showed that the drug bortezomib is able to impair spontaneous lung metastasis in mice, suggesting that this drug can inhibit the formation of distant metastasis. As an alternative to mouse experiments, we started to use zebrafish embryos for our investigations. We could demonstrate that as few as 50–200 injected CTCs faithfully extravasate and proliferate in zebrafish embryos highlighting its value for functional and drug-target discovery.
