480P - Clinical utility of ctDNA detection by NGS for diagnosis of CNS lymphoma

Background

The diagnosis of CNS lymphoma (CNS-L) is routinely based on cranial MRI along with brain excisional biopsy or analysis of cerebrospinal fluid (CSF) by cytology and flow cytometry (FC). However, these methods often provide inconclusive results. Recently, ctDNA detection by NGS in the CSF has emerged as a valuable tool for prognosis and treatment guidance.

Methods

This study assesses the clinical utility of ctDNA detection and monitoring by NGS in CSF for a cohort of lymphoma patients at risk of or diagnosed with CNS infiltration. CSF supernatants from 11 patients were studied: 4 CNS-L; 6 systemic DLBCL and 1 FL with isolated CNS relapse. A custom NGS panel containing the 56 most relevant mutated genes in lymphoma B malignancies was applied. NGS result was compared with available gold standard methods: MRI, FC and cytology.

Results

NGS panel detected lymphoma-related mutations in all samples. An average of 12 variants per patient with VAFs ranging from 1.1 to 95.7% were detected. The most frequently mutated genes were EP300, KMT2D, CD79B, PIM1, MYD88, NOTCH1, CIITA and ARID1A. Three NGS-ctDNA positive patients had also confirmed CNS infiltration by FC/cytology and RMI. The other 8 patients had positive NGS-ctDNA but discordant result by standard techniques. Six out of 8 patients showed MRI compatible with CNS infiltration but inconclusive result by FC or cytology. In this subset the NGS-ctDNA detection played an important role to diagnose infiltration and establishing a specific treatment, resulting in a favorable response for all patients. In the remaining 2, brain biopsy was required for diagnosis. NGS-ctDNA seems to be crucial for an accurate diagnosis considering that FC provided 73% of false negative results. Lastly, NGS-ctDNA was evaluated in 3 patients during follow-up. One was ctDNA-NGS positive confirming disease progression. The remaining 2 were NGS-ctDNA negative and both patients are currently disease-free.

Conclusions

These results highlight the importance of CSF analysis by NGS, postulating as a transformative tool for improving diagnosis, monitoring and outcome of CNS-L patients. Since NGS surpassed in some cases the capabilities of traditional methods, CSF should be preferably analyzed by NGS in the clinical practice.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

A. Jiménez-Ubieto.

Funding

Fundación CRIS contra el cáncer.

Disclosure

All authors have declared no conflicts of interest.