Divergence of DNA tumor mutations in cerebrospinal fluid in metastatic breast cancer patients with leptomeningeal metastases.

Breast cancer patients with confirmed or probable LM and available primary tumor tissue were selected from a CSF-biobank study of the Netherlands Cancer Institute. Genetic analysis of cell-free DNA (cfDNA) in CSF and tissue from the primary tumor and/or systemic metastases was performed using Next Generation Sequencing (NGS). In patients with HR+/HER2-breast cancer, CSF and tumor tissues were also tested for ESR1 mutations with Sanger sequencing.

In 20 % of breast cancer patients with LM, genetic alterations in the CSF were discordant from the primary tumor and/or systemic metastases. These genetic alterations involved in particular the PTEN-PI3K-AKT pathway in TN breast cancer. No ESR1 mutation limited to CSF only was found in HR+/HER2-breast cancer. Divergence of genetic alterations in LM from breast cancer must be considered for optimization of future target treatment strategy.

27 breast cancer patients with LM (n = 23 confirmed LM; n = 4 probable LM) were included in the study. Fourteen patients had triple negative (TN), 11 HR+/HER2-and 3 HER2+ breast cancer. CSF-only genetic alterations were observed in 5 (20 %) of 25 evaluable patients. The majority of these genetic alterations were found in the PTEN-PI3K-AKT pathway, which were present in 3 of 14 evaluable patients with a TN breast cancer subtype (21 %) and in one patient wit HER2+ breastcancer. In one HR+/HER2+ patient, an ESR1 mutation was present in both CSF and systemic metastases, while it was absent in the primary tumor. All genetic alterations that were observed in either the primary tumor or systemic metastases were also observed in the CSF.

To study differences in genetic alterations between primary breast cancer, systemic metastases, and cerebrospinal fluid (CSF) in patients with leptomeningeal metastases (LM).