Trop-2 expression on treatment resistant cancer cells in castrate-resistant prostate cancer (CRPC) as a predictive biomarker for targeted therapy

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Background: Trophoblastic cell-surface antigen (Trop-2) is a transmembrane glycoprotein that is highly expressed in many solid tumors. Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate of an anti-Trop-2 humanized antibody with SN-38. Early clinical trials have shown high response rates in a broad range of diseases including triple negative breast and urothelial cancers. We evaluated Trop-2 expression in tumor biopsies and circulating tumor cells (CTCs) from men with mCRPC (metastatic castrate-resistant prostate cancer). Methods: Trop-2 expression was evaluated from mCRPC biopsies from patients (Pts) treated with abiraterone acetate (AA) on the PROMOTE clinical trial, CTCs from a separate cohort treated with either enzalutamide or AA. Trop-2 CTCs were compared with EpCAM captured CTCs using a microscale technology termed the VERSA (Vertical Exclusion-based Rare Sample Analysis) platform to compare protein and gene expression signatures of resistance to these agents. Results: RNA sequencing identified Trop-2 gene expression in > 70% of metastatic biopsies. The AR splice variant V7 was found in 48 biopsies that also expressed Trop-2. Trop-2 expression was not altered by treatment with AA at 12 weeks. The number of CTCs captured from 25 pts with Trop-2 or EpCAM were closely correlated (R2= 0.84). Gene expression analysis showed similar patterns of expression for the TROP-2 and EPCAM captured cells. AR splice variant expression (AR-V7, AR-V9) in Trop-2 and EpCAM CTCs was detected in 33% of patients. Expression of neuroendocrine markers was identified in 40% of Trop-2 CTCs. Conclusions: Trop-2 is frequently expressed in mCRPC and co-expressed in tumors that express AR splice variants. Trop-2 CTCs are detected in CRPC pts previously treated with AA or Enzalutamide that also express multiple AR splice variants and neuroendocrine markers. The results support Trop-2 expression as predictive biomarker of sensitivity to targeted therapies tumors resistant to AA or Enzalutamide. Men with mCRPC are being enrolled on a Phase I trial with IMMU-132, and multi-site Phase II clinical trial in men who have progressed on AA or Enzalutamide is being finalized.

Survival outcomes of patients with metastatic germ cell tumor (mGCT) treated from 1998 to 2012: The Indiana University (IU) experience

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Background: Patients with mGCT’s treated between 1975-1990 were classified by the International Germ Cell Cancer Collaborative Group (IGCCCG) into good, intermediate, and poor risk. This study attempts to identify prognostic factors in a contemporary cohort of patients with mGCT treated at IU. Methods: Retrospective analysis of all patients with GCT seen at IU from 1998-2012. 1,341 consecutive patients with mGCT were identified of whom 615 patients received initial chemotherapy at IU and were eligible for analysis. All patients in this cohort were treated with cisplatin-based combination chemotherapy. Kaplan-Meier methods were used for analysis of 5 year progression free survival (PFS) and overall survival (OS). Results: Median age was 29. Median follow up time 5 years. Good, intermediate, and poor risk disease had median AFP of 8, 1822, 291 and median hCG of 8, 5000, 12837 respectively. 89 (14%) patients had seminoma and 526 (86%) had non-seminomatous GCT (NSGCT). Primary site was testis/retroperitoneal in 565 (92%) and mediastinum in 48 (8%). The 5 year PFS and OS for patients with poor risk excluding primary mediastinal NSGCT (PMNSGCT) was 52% and 78% respectively. In contrast, 5 year PFS and OS for patients with PMNSGCT was 49% and 58% respectively. The results comparing outcomes of patients in IGCCCG versus patients at IU are depicted in the table below. Conclusions: In this contemporary retrospective dataset from Indiana University there was improvement in OS for men with poor risk mGCT, possibly due to improved salvage chemotherapy. Only patients with PMNSGCT continue to have poor outcomes and pose a therapeutic challenge due to lack of effective salvage therapy. [Table: see text]