The Initial Detection and Partial Characterization of Circulating Tumor Cells in Neuroendocrine Prostate Cancer

Abstract

Background The transition of prostate adenocarcinoma to a predominantly androgen receptor (AR) signaling independent phenotype can occur in the later stages of the disease and is associated with low AR expression and/or the development of small cell or neuroendocrine tumor characteristics. As metastatic tumor biopsies are not always feasible and are difficult to repeat, we sought to evaluate noninvasive methods to identify patients transitioning towards a neuroendocrine phenotype (NEPC). Experimental Design We prospectively studied a metastatic tumor biopsy, serum biomarkers and circulating tumor cells (CTC, Epic Sciences) from patients with castration resistant prostate cancer (CRPC) including those with pure or mixed NEPC histology present on biopsy. CTCs labeled with the patient’s clinical status were used to learn features that discriminate NEPC patients, which was then applied to an independent cohort. Results Twenty-seven patients with CRPC including 12 NEPC and 5 with atypical clinical features suggestive of NEPC transition were studied. CTCs from NEPC patients demonstrated frequent clusters, low or absent AR expression, lower cytokeratin expression, and smaller morphology relative to typical CRPC. A multivariate analysis of protein and morphologic variables enabled distinguishing CTCs of NEPC from CRPC. This CTC classifier was applied to an independent prospective cohort of 159 metastatic CRPC patients and identified in 17/159 (10.7%) of cases, enriched in patients with high CTC burden (p<0.01) and visceral metastases (p=0.04). Conclusions CTCs from patients with NEPC have unique morphologic characteristics, which were also identified in a subset of CRPC patients with aggressive clinical features potentially undergoing NEPC transition.

Phenotypic Heterogeneity of Circulating Tumor Cells Informs Clinical Decisions between AR Signaling Inhibitors and Taxanes in Metastatic Prostate Cancer

“…These positive selection methods often miss critical CTC subtypes and do not consistently assess cell features essential to the analysis of heterogeneity. The CAP-accredited and CLIA-certified Epic Sciences platform used here has undergone the necessary analytical validation (accuracy, linearity, specificity, and intra/inter-assay precision) for CTC detection and enumeration (26) and has been previously demonstrated to detect a wide range of CTC phenotypes (32,33,40,43). These include rare CTCs that are negative for epithelial markers with malignant genomics (40,43) and CTCs that are smaller than WBCs (32,43).…”

“…Red blood cells were lysed, and approximately 3 million nucleated cells were dispensed onto 10–16 glass microscope slides and placed at −80 °C for long-term storage as previously described (26,32,33). Sample processing and testing were conducted in laboratories following both Clinical Laboratory Improvement Amendments (CLIA) and College of American Pathologists (CAP) regulations.…”

“…CTCs were characterized by automated immunofluorescent staining for DAPI (a DNA stain), cytokeratins, CD45 (hematopoietic lineage marker), and AR N-terminal domain (AR) (Cell Signaling D6F11) as previously described (26,32,33). Up to two slides were evaluated per sample tested.…”

CTC-derived AR-V7 detection as a prognostic and predictive biomarker in advanced prostate cancer

“…Although this may be a limitation of EPCAM-based CTC assays, CTCs have been identified in AR-low prostate cancer cells using non-EPCAM based tests), including neuroendocrine prostate carcinomas 36 . Also, AR-V7 has been identified in AR-low prostate cancer such as neuroendocrine carcinomas 37 .…”

A Prominent Couple

“…CTCs in blood samples from patients with confirmed small cell carcinoma were shown to be positive for CD56 and were of smaller size than CTCs from CRPC patients. This study highlights the phenotypic similarities between tumor and CTCs and suggests potential use of CTCs in the early detection of PCa transforming towards NEPC [148]. However, so far only increased CTC count was prospectively validated in two phase III randomized trials, showing association with reduced overall survival [149,150].…”