Wang, Xiaohong

Abstract Background Cerebrospinal fluid cell-free DNA (cfDNA) can detect and monitor leptomeningeal disease but has not been previously used to monitor parenchymal lesions. Methods Herein, we report our initial experience with CSF cfDNA monitoring for 2 patients with colorectal cancer (CRC) metastases to the thalamus, causing obstructive hydrocephalus. Results CSF samples were obtained during ventriculoperitoneal shunt placement, demonstrating high levels of cfDNA in both cases. Several genomic alterations detected in the cfDNA sequencing matched those in the tumor tissue biopsy. Follow-up CSF evaluations after subsequent therapy were used to help adjudicate pseudo-progression versus true progression. Conclusions Neither patient developed leptomeningeal disease, demonstrating CSF’s utility in evaluating solitary brain metastases in direct contact with a CSF compartment.

176 Background: Multiple tumour tissue studies have demonstrated the prognostic utility of CNVs in mCRPC. However, accurate assessment of CNVs in plasma cfDNA remains challenging, and prognostic significance has not been well characterized. Using a large customized panel, we correlated plasma CNVs with clinical outcomes in a contemporary cohort of mCRPC patients. Methods: Deep targeted sequencing was performed using a 180-gene cfDNA panel (Predicine) in 56 patients commencing AR pathway inhibitors (enzalutamide or abiraterone; n = 34) or taxane chemotherapy (n = 22) at two Australian institutions. Kaplan-Meier estimates and Cox proportional-hazards models were used to correlate CNVs with progression-free survival (PFS) and overall survival (OS). Significant results were validated in an independent cohort (Mayo Clinic, n = 144). Results: Median follow-up was 19.4 months (mo; IQR 11.3-31.9). The most common CNVs in the Australian cohort are shown (Table). OS was significantly decreased in patients with PI3KCA gain (median 21.7 mo vs 6.6 mo, p < 0.0001), PTEN loss (24.8 mo vs 11.7 mo, p = 0.0019) and AR gain (21.7 mo vs 12.0 mo, p = 0.0083). Furthermore, all three alterations independently predicted for poor survival in multivariable analyses (MVA; Table). Findings in the independent cohort showed similar OS results in MVA: PIK3CA gain (HR 2.0, p = 0.07), PTEN loss (HR 1.7, p = 0.08) and AR gain (HR 1.7, p = 0.03). Conclusions: Sequencing of plasma cfDNA revealed that PTEN loss, and PIK3CA and AR gain are associated with inferior clinical outcomes in patients commencing contemporary systemic treatment. These data support therapeutic strategies co-targeting the PI3K and AR pathways in mCRPC.[Table: see text]