Morphology-predicted, large-scale transition (LST) number in circulating tumor cells (CTC) as a biomarker of chromosomal instability (CIN) to assess early resistance to standard of care (SOC) drugs in mCRPC.

Abstract

225 Background: CIN is a mechanism by which tumor cells evolve, adapt, and evade therapeutic insults. We explored the relationship between the presence of LST as a biomarker of CIN through distinct CTC phenotypes, and sensitivity of tumors with the biomarker to standard of care (SOC) drugs. Methods: CTCs from 634 mCRPC blood samples were morphologically characterized by the Epic Sciences platform [Cytokeratin, CD45, DAPI, Androgen Receptor (AR) staining]. Training: 20 digital single cell image features were extracted from 608 CTC images from 26 patients (Pts) and single cell sequenced to determine the number of genomic LSTs. An image feature based algorithm to predict whether the number of LSTs was above the normal range defined by analysis of leukocytes was trained using this cohort (pLST) and parameters were locked. Analytical Validation (AV): the pLST algorithm was applied to a separate cohort of 570 CTCs from 54 Pts that were also sequenced to test single cell analytical performance. Clinical Validation: The pLST algorithm was then applied to CTC detected in 554 Pt samples obtained at prior to (BL, n= 324) and matched on-therapy (OnTx, n= 230) ~1 mo after starting SOC [including AR directed Tx and taxane]. A pre-defined patient scoring of > 3 pLST+ CTC/mL was related to PSA kinetics, time on drug, and overall survival (OS). Results: pLST identifies CTCs with a high number of genomic LSTs. Pts with pLST+ at BL or OnTx had poor survival (see table): 12/13 pts receiving ARSi’s and 17/18 pts receiving taxanes who were pLST+ On-Tx required a change of Tx in a median of 1.3 mo (0.9 to 2.1) or died within 6 mo. Conclusions: CTC morphology can be used to predict CIN as defined by high LSTs. CTC pLST is a strong marker of resistance to SOC Tx in mCRPC pts and treatment failure requiring a change in Tx earlier than standard criteria.[Table: see text]