Cancer micrometastases

Micrometastatic disease and metastatic outgrowth: clinical issues and experimental approaches

Metastasis from the primary tumor to distant organs is the principal cause of mortality in patients with cancer. While prognostic factors can predict which patients are likely to have their cancer recur, these are not perfect predictors, and some patient's cancers recur even decades after apparently successful treatment. This phenomenon is referred to as dormancy. Data from experimental studies have revealed two categories of metastatic dormancy: cellular dormancy, with solitary cancer cells in cell-cycle arrest; and micrometastatic dormancy, characterized by a balanced state of proliferation and apoptosis, but with no net increase in size. Development of new models and imaging techniques to track the fate of dormant cancer cells is beginning to shed some light on dormancy. Elucidation of the molecular pathways involved in dormancy will advance clinical understanding and may suggest new avenues for treatment to inhibit the revival of these dormant cells, thereby reducing cancer mortality rates.

Significance of Circulating Tumor Cells Detected by the CellSearch System in Patients with Metastatic Breast Colorectal and Prostate Cancer

The increasing number of treatment options for patients with metastatic carcinomas has created a concomitant need for new methods to monitor their use. Ideally, these modalities would be noninvasive, be independent of treatment, and provide quantitative real-time analysis of tumor activity in a variety of carcinomas. Assessment of circulating tumor cells (CTCs) shed into the blood during metastasis may satisfy this need. We developed the CellSearch System to enumerate CTC from 7.5 mL of venous blood. In this review we compare the outcomes from three prospective multicenter studies investigating the use of CTC to monitor patients undergoing treatment for metastatic breast (MBC), colorectal (MCRC), or prostate cancer (MPC) and review the CTC definition used in these studies. Evaluation of CTC at anytime during the course of disease allows assessment of patient prognosis and is predictive of overall survival.

Dormancy of metastatic melanoma

Metastatic dormancy of melanoma has not received sufficient attention, most likely because once detectable, metastasis is almost invariably fatal and, understandably, the focus has been on finding ways to prolong life of patients with overt recurrences. Nevertheless, analysis of the published clinical and experimental data on melanoma indicates that some aspect of melanoma biology imitate traits recently associated with dormancy in other solid cancers. Among them the ability of some melanomas to disseminate early during primary tumor progression and once disseminated, to remain undetected (dormant) for years. Comparison of cutaneous and uveal melanoma indicates that, in spite of being of the same origin, they differ profoundly in their clinical progression. Importantly for this discussion, between 40 and 50% of uveal melanoma remain undetected for longer than a decade, while less than 5% of cutaneous melanoma show this behavior. Both types of melanoma have activating oncogene mutations that provide autonomous pro-proliferative signals, yet the consensus is that those are not sufficient for tumor progression. If that is the case, it is possible to envision that signals from outside the tumor cell, (microenvironment) shape the fate of an individual disseminated cell, regardless of an oncogene mutation, to progress or to pause in a state of dormancy. To stimulate further debate and inquiry we describe here a few examples of potential signals that might modify the fate of disseminated cell and provide brief description of the current knowledge on dormancy in other cancers. Our hope is to convince the reader that disseminated melanoma cells do enter periods of prolonged dormancy and that finding ways to induce it, or to prolong it, might mean an extension of symptoms-free life for melanoma patients. Ultimately, understanding the biology of dormancy and the mechanisms of dormant cell survival, might allow for their specific targeting and elimination.

Tumor and host-mediated pathways of resistance and disease progression in response to antiangiogenic therapy

Despite early benefits seen in cancer patients treated with antivascular endothelial growth factor (VEGF) pathway-targeted drugs, the clinical benefits obtained in terms of progression-free or overall survival have been more modest than expected. This outcome is, at least in part, due to antiangiogenic drug resistance mechanisms that involve pathways mediated largely by the tumor, whether intrinsic or acquired in response to therapy, or by the host, which is either responding directly to therapy or indirectly to tumoral cues. The focus of this review is to distinguish, where possible, between such host and tumor-mediated pathways of resistance and discuss key challenges facing the preclinical and clinical development of antiangiogenic agents, including potential differences in drug efficacies when treating primary tumors or various stages of metastatic disease.

Full-length cytokeratin-19 is released by human tumor cells: a potential role in metastatic progression of breast cancer

Introduction

We evaluated whether CK19, one of the main cytoskeleton proteins of epithelial cells, is released as full-length protein from viable tumor cells and whether this property is relevant for metastatic progression in breast cancer patients.

Methods

EPISPOT (EPithelial ImmunoSPOT) assays were performed to analyze the release of full-length CK19 by carcinoma cells of various origins, and the sequence of CK19 was analyzed with mass spectrometry. Additional functional experiments with cycloheximide, Brefeldin A, or vincristine were done to analyze the biology of the CK19-release. CK19-EPISPOT was used to detect disseminated tumor cells in bone marrow (BM) of 45 breast cancer patients who were then followed up over a median of 6 years.

Results

CK19 was expressed and released by colorectal (HT-29, HCT116, Caco-2) and breast (MCF-7, SKBR3, and MDA-MB-231) cancer cell lines. The CK19-EPISPOT was more sensitive than the CK19-ELISA. Dual fluorescent EPISPOT with antibodies against different CK19 epitopes showed the release of the full-length CK19, which was confirmed by mass spectrometry. Functional experiments indicated that CK19 release was an active process and not simply the consequence of cell death. CK19-releasing cells (RCs) were detectable in BM of 44% to 70% of breast cancer patients. This incidence and the number of CK19-RCs were correlated to the presence of overt metastases, and patients with CK19-RCs had a reduced survival as compared with patients without these cells (P = 0.025, log-rank test; P = 0.0019, hazard ratio, 4.7; multivariate analysis).

Conclusions

Full-length CK19 is released by viable epithelial tumor cells, and CK19-RCs might constitute a biologically active subset of breast cancer cells with high metastatic properties.