Morphological Subsets of Circulating Tumor Cells in Advanced Prostate Cancers: A Potential Biomarker for Patients with Visceral Metastases

Abstract

Circulating tumor cells (CTCs) are commonly identified in men with advanced prostate cancer (PC) but their significance beyond enumeration is unknown. We subclassified CTCs using a standard pathology approach and focused on the correlation between CTC subsets and visceral metastasis (VM) in advanced PC. We obtained blood samples from 50 PC patients across the spectrum of metastatic states. The patients were divided into training and validation cohorts. CTCs were captured and enumerated on NanoVelcro Chips and were subjected to pathologic review for cellular morphology and nuclear size. The nuclear size distribution was analyzed using a Gaussian Mixture Model, which revealed 3 distinct subpopulations in the training cohort: large-nuclear CTCs, small-nuclear CTCs, and very-small-nuclear CTCs (vsnCTCs). Subsequent correlational analyses revealed elevated vsnCTC counts in PCs with VM when compared to those without (p=0.005). This difference remained statistically significant in the validation cohort (p=0.007). Serial enumerations showed emergence of vsnCTCs prior to detection of newly developed VM. From these data we concluded that CTC subsets contain relevant information on PC disease status when analyzed with pathologic approaches such as nuclear size assessment. In particular, the detection of vsnCTCs correlated with the presence of VM and should be explored as a potential biomarker to identify patients at risk for developing this more aggressive form of PC.