Optimizing the diagnosis of leptomeningeal metastases in breast cancer patients by circulating tumor cells and circulating tumor dna

Abstract Introduction: Leptomeningeal metastases (LM) occur in approximately 5% of patients with breast cancer, negatively impacting their prognosis. Reliable diagnosis of LM is challenging, but timely diagnosis could lead to more treatment options and consequently a better prognosis. Circulating tumor DNA (ctDNA) and circulating tumor cells (CTCs) in cerebrospinal fluid (CSF) are potential methods to improve the diagnosis of LM. In this prospective study we compared cytology (current gold standard for CSF analysis in diagnosing LM) with CTC enumeration and ctDNA detection in CSF for diagnosing LM in patients with breast cancer. Methods: In a prospective study in patients with clinical suspicion of LM who were planned to undergo a diagnostic lumbar puncture (LP) for CSF cytology the presence of CTCs/ctDNA in CSF was compared to the presence of tumor cells in CSF by cytology. CTC enumeration was performed using the FDA approved CellSearch System (Menarini). The detection of ctDNA was performed using the mFAST-Seqs method, which detects aneuploidy throughout the genome by selective amplification of long interspaced nuclear element sequences (LINE-1 elements). In a control group consisting of 15 patients with a hematologic malignancy with suspicion of LM, 2 cases had 1 CTC in their CSF, therefore the cutoff for a positive CTC test was set at 2 CTCs. Results: In total 80 patients with breast cancer were included from January 2016 till January 2022. In 16 out of 80 patients CSF cytology was positive of whom 14 (87.5%) had a positive CTC test. From the 2 patients in which the CTC test was negative, one patient had 1 CTC detected in CSF and for both patients a lower volume of CSF was available for the CTC test compared to the volume used for cytology. In 2 of the 16 cytology positive patients, who underwent a second LP, CTCs were positive in the CSF from the first LP, while cytology was only positive in the CSF of the second LP. Of the 64 patients with a negative cytology, 7 (10.9%) patients had a positive CTC test. Two of these 7 patients had typical symptoms of LM, a suspicious MRI and a course of disease matching with LM according to the neuro-oncologist. Overall survival (OS) was shorter in patients with a positive CTC test compared to patients with a negative test (median OS: 19.2 months vs. 3.4 months, log-rank test, p=0.007). When only patients with a negative cytology were included in this analysis, OS remains significantly shorter in the group with a positive CTC test (n=7) compared to the group with the negative CTCs (n=57) (median OS 19.3 months vs. 3.5 months, long-rank test, p=0.003). Additionally, ctDNA detection in CSF was compared to CSF cytology in 51 patients, of which 11 had a positive CSF cytology result. For 8 of these 11 patients ctDNA was detected (72.2%) while 1 of the 40 patients with a negative cytology had ctDNA. Discussion: Both CTC enumeration and ctDNA detection can be used to detect LM in CSF. CTC detection could even improve timely diagnosis of LM in patients with breast cancer. However, the added value of ctDNA seems less evident. Citation Format: Elisabeth M Jongbloed, Lindsay Angus, Martin J van den Bent, Joost LM Jongen, John WM Martens, Ngoc M Van, Vanja de Weerd, Carolien HM van Deurzen, Jaco Kraan, Saskia M Wilting, Agnes Jager. OPTIMIZING THE DIAGNOSIS OF LEPTOMENINGEAL METASTASES IN BREAST CANCER PATIENTS BY CIRCULATING TUMOR CELLS AND CIRCULATING TUMOR DNA [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-05-23.