Circulating tumor cell (CTC) enumeration in patients with metastatic neuroendocrine prostate cancer (NEPC) and castration-resistant prostate cancer (CRPC).

Abstract

204 Background: Neuroendocrine prostate cancer (NEPC) is an aggressive variant of prostate cancer. Circulating tumor cell (CTC) counts as measured by CellSearch are prognostic for large groups with metastatic prostate cancer (PC), but are not well described in NEPC. Methods: With institutional review board approval, we retrospectively identified patients with metastatic PC and available CTC enumeration (CellSearch methodology) and compared counts/7.5 mL blood and overall survival (OS), measured from the first recorded CTC count until death or last follow up. Entry criteria for clinical trials were used to define NEPC, including histology (small cell/neuroendocrine carcinoma or adenocarcinoma with more than 50% NE staining), serum chromogranin greater than 5x ULN and/or neuron specific enolase greater than 2x ULN, and/or predominant liver/brain metastases with lack of prostate-specific antigen [Beltran ASCO 2013, clinicaltrials.gov NCT01799278 ]. Frequency of detectable and unfavorable counts was tabulated and OS was compared across groups. Results: Sixty one patients were identified: 21 NEPC with median age 73.7 and 40 patients with castration-resistant prostate cancer (CRPC) with median age 73.9 over contemporary time periods 2009 to 2012. Median OS for the entire group was 22.6 months (mo), with a trend for shorter OS in NEPC (20.7 mo) than CRPC (22.7 mo), p=0.11. 47.6% of NEPC and 55% of CRPC had detectable CTC counts (p=0.58); 38.1% of NEPC and 40.0% of CRPC had greater than or equal to five CTCs (p=0.89). CTC counts of 0 to 4 versus greater than or equal to five were prognostic for both groups: NEPC with 0 to 4 CTCs had median OS of 22.6 versus 6.6 mo for CTCs greater than or equal to 5 (p<0.001) and CRPC with 0 to 4 CTCs median OS not reached (mean 40.6 mo) versus 11.2 mo for those with greater than or equal to five CTCs (p<0.001). Conclusions: Patients with NEPC have similar frequency of detectable and elevated CTC counts by CellSearch methodology as compared to an overall CRPC population. CTC counts are prognostic for both groups.