Association of very small nuclear circulating tumor cell (vsnCTC) with clinical outcomes in metastatic castration-resistant prostate cancer.

Abstract

168 Background: Circulating tumor cells (CTCs) have arisen as contemporary noninvasive prognostic biomarkers for prostate cancer (PC). Previously, a subgroup of PC CTCs, with particularly small nuclei (<8.5 μm), were found to be correlated with the presence of visceral metastases. This subgroup was named very-small-nuclear CTCs (vsnCTCs). We proposed vsnCTCs as a putative biomarker of a lethal subtype in metastatic castration resistant PC (mCRPC). Methods: In this study, 76 patients with mCRPC were recruited for overall survival (OS) analysis. Of the 76 patients, 47 had available pre-treatment blood specimens prior to the initiation of androgen receptor signaling inhibitor (ARSI, e.g. abiraterone and enzalutamide) or taxane therapy. Using the NanoVelcro CTC Assay, CTCs were captured and subjected to immunofluorescence staining. CTCs were identified as DAPI+/CK+/CD45- with a round or oval nucleus. Additionally, CTC nuclear size was measured and defined as the square root of the product of the long axis and the short axis. Kaplan-Meier analysis and Cox proportional hazards model were conducted. Results: Patients with vsnCTC (i.e., vsnCTC+) had a significantly shortened OS compared with patients without vsnCTC (i.e., vsnCTC-). The median OS was 34 (vsnCTC+, n=49) vs. 149 (vsnCTC-, n=27) weeks (log-rank HR=2.6 with 95% CI 1.5 to 4.5, p=0.0006). Progression free survival (PFS) analysis was performed for the 47 patients with pre-treatment blood samples. The median PFS was 14 (vsnCTC+, n=29) vs. 26 (vsnCTC-, n=18) weeks (log-rank HR=2.2 with 95% CI 1.2 to 3.9, p=0.0069). We also found that the hazard ratio of overall survival increased significantly as the CTC nuclear size decreased using the p spline plot. Conclusions: Our study showed that nuclear size reduction has importance in CTCs in a fashion similar to its utility in tissue. This study points toward the importance of the vsnCTC in patients with mCRPC, as vsnCTC+ patients represented a group at risk for faster clinical progression who are at the highest risk for morality. We posit that the vsnCTC represents a new hallmark of an aggressive subtype of mCRPC. This has potential importance in optimizing therapeutic choices.