ESTRO 2024 - Abstract Book

S2423

Clinical - Urology

ESTRO 2024

1324

Poster Discussion

Role of CTC in oligometastatic prostate cancer: results of ADAPT-CTC prospective trial

Fabio Matrone 1 , Matteo Turetta 2 , Marcella Montico 3 , Agostino Steffan 2 , Roberto Bortolus 1 , Lucia Fratino 4 , Alessandra Donofrio 1 , Veronica Paduano 5 , Martina Zanchetta 3 , Fabio Del Ben 2 , Giulia Brisotto 2 1 Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Department of Radiation Oncology, Aviano, Italy. 2 Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Immunopathology and Cancer Biomarkers Units, Department of Cancer Research and Advanced Diagnostics, Aviano, Italy. 3 Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Clinical Trial Office, Scientific Direction, Aviano, Italy. 4 Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Department of Medical Oncology, Aviano, Italy. 5 Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, CRO Biobank, Aviano, Italy

Purpose/Objective:

The identification of novel biomarkers that can improve the prognostic stratification of oligometastatic prostate cancer (OMPC) patients undergoing Stereotactic Body Radiation Therapy (SBRT) is an unmet clinical need [1,2]. Liquid biopsy-based biomarkers, such as Circulating Tumor Cells (CTC), have emerged as a promising minimally invasive tool for predicting patient prognosis [3]. The aim of our study was to evaluate whether CTC can be detected in these patients and to assess whether CTC level correlates with clinical outcome

Material/Methods:

We conducted a pilot, prospective, observational study (ADvanced Approach to ProsTate cancer-Circulating Tumor Cells, ADAPT-CTC; registration number: CRO-2019-68) in patients affected by metachronous hormone-sensitive OMPC. Linac-based SBRT, total dose of 30-35 Gy in 3-5 daily fractions, was administered to 1-3 nodal and/or bone metastases detected by Choline- or PSMA-PET. Patients were allowed to have received ADT for biochemical relapse after primary treatment but not within 6 months before baseline evaluation. CTC were detected with a novel metabolism-based assay, able to identify CTC by their hypermetabolic behavior [4]. Peripheral blood samples (7.5 ml in EDTA-tube) were collected before the start of SBRT (T0), 1 (T1) and 3 months (T2) after SBRT.

Results:

A total of 34 patients were enrolled (clinical characteristics in Table 1). Median [range] CTC were 5 [0-44], 8 [0-194] and 4 [0-426] at T0, T1, and T2, respectively. Patients with at least 1 CTC at T0, T1, and T2 were 82.3%, 77.4% and 75.0%, respectively. No significant difference in CTC levels among time points was detected. The levels of CTC did not correlate with PSA at the different time points. After a median follow up of 25.6 months, distant progression was registered in 20 patients of whom 14 underwent a new oligometastatic progression, with a median Distant Progression- Free Survival (DPFS) of 16.7 months. A high CTC level at T0 (defined as CTC ≥5) was associated with a decreased DPFS compared with low CTC level (defined as CTC<5) (11.1 months vs not-reached, p=0.024; Fig. 1). At univariate analysis, CTC level at T0 (low vs high) (HR 2.77, 95% CI 1.1-7.0, p-value=0.03) and number of metastatic