Detection and Characterization of Circulating Tumor Cells in Patients with Merkel Cell Carcinoma

Abstract

BACKGROUND Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer with increasing incidence and high mortality rates. MCC has recently become the subject of immune checkpoint therapy, but reliable biomarkers for estimating prognosis, risk stratification, and prediction of response are missing. METHODS Circulating tumor cells (CTCs) were detected in peripheral blood from patients with MCC by use of the CellSearch® system. Moreover, CTCs of selected cases were characterized for Merkel cell polyomavirus (MCPyV), chromosomal aberrations, and programed death ligand 1 (PD-L1) production. RESULTS Fifty-one patients were tested at first blood draw (baseline), and 16 patients had 2 or 3 consecutive measurements to detect CTCs. At baseline, ≥1 CTC (range, 1–790), >1, or ≥5 CTCs/7.5 mL were detected in 21 (41%), 17 (33%), and 6 (12%) patients, respectively. After a median follow-up of 21.1 months for 50 patients, detection of CTCs correlated with overall survival (≥1, P = 0.030; >1, P < 0.020; and ≥5 CTCs/7.5 mL, P < 0.0001). In multivariate Cox regression analysis, the detection of ≥5 CTCs/7.5 mL adjusted to age and sex compared to that of <5 was associated with a reduced overall survival (P = 0.001, hazard ratio = 17.8; 95% CI, 4.0–93.0). MCPyV DNA and genomic aberrations frequently found in MCC tissues could also be detected in single CTCs. Analyzed CTCs were PD-L1 negative or only weakly positive. CONCLUSIONS The presence of CTCs is a prognostic factor of impaired clinical outcome, with the potential to monitor the progression of the disease in real time. Molecular characterization of CTCs might provide new insights into the biology of MCC.

Circulating Tumor Cell Detection and Polyomavirus Status in Merkel Cell Carcinoma

“…Two previous studies on CTC detection in MCC with the CellSearch system identified CTCs in 41% of the tested patients 27,28 . On the other hand, the Maintrac technology, based on the EpCAM/CD56 or CK20 markers for CTC detection, identified CTCs in up to 90% of patients.…”

“…In addition, CTCs have been included as prognostic markers in MCC. Three recent studies addressed CTC detection in MCC [26][27][28] , two using positive selection strategy for CTC enrichment before their detection and one using erythrocytes lysis. Conversely, our study compared two different complementary methods for CTC detection in MCC: (i) the CellSearch system, the only FDA-cleared technology for metastatic breast, prostate and colon cancer [17][18][19] , and (ii) the RosetteSep and DEPArray (R-D) workflow, where CTC detection is based on negative enrichment (leukocyte depletion) followed by CTC detection by DEPArray that also allows the direct sorting of single CTCs.…”

“…One study correlated the presence of miR-375 in serum of patients with MCC 23 , some others determined T antigen antibodies as a prognostic marker in MCC 24,25 and only three studies have investigated CTC detection in MCC: two based on EpCAM-positive selection of CTCs using the CellSearch system and one using the Maintrac system [26][27][28] . These three studies found that CTC detection in MCC is feasible, and one also reported that the presence of CTCs is a prognostic factor of worse clinical outcome 28 . As the biology of MCC CTCs is not yet fully understood, we decided to detect CTCs without any bias of selection for the enrichment step.…”

Current progress in the clinical use of circulating tumor cells as prognostic biomarkers

“…These include immunoaffinity analysis (for markers including EpCAM, CD15, CD45, and CD66b); techniques for the analysis of biophysical characteristics such as size, deformability, density, and surface charge; immunofluorescence for quantification; and molecular techniques including sequence analysis for genomics and transcriptomics, mass cytometry for proteomic analysis, and targeted bisulfite sequencing for epigenetic analysis . Table highlights the potential of CTCs as biomarkers for disease progression, prognosis, and outcomes for a wide range of cancers . Figure summarizes the potential prognostic role of CTCs at various stages of cancer.…”

“…4 Table 1 highlights the potential of CTCs as biomarkers for disease progression, prognosis, and outcomes for a wide range of cancers. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] Figure 1 summarizes the potential prognostic role of CTCs at various stages of cancer.…”