This study will prospectively enroll 36 evaluable subjects with breast cancer who are undergoing workup for clinical suspicion of leptomeningeal metastasis (LM). Neuroimaging consisting of MRI of the brain or total spine (or both, as clinically indicated) will be obtained in all patients. Patients will also undergo a lumbar puncture and standard CSF evaluation, which may consist of intracranial pressure measurement, CSF protein, glucose, white and red cell analysis, infectious cultures, as well as conventional cytopathologic analysis (cytocentrifuge). An additional CSF sample will be obtained for evaluation of CSF CTCs by OncoCEETM technology and cell-free DNA (recommended amount: 1 tube, 10 mL) at the time of lumbar puncture.

Leptomeningeal metastasis (LM) is a condition in which cancer cells seed the meninges and may go on to invade the brain parenchyma, spinal cord, cranial nerves or peripheral nerves. It is a devastating complication of breast cancer, and is often considered in the differential diagnosis when patients with breast cancer present with new neurologic symptoms. It was previously thought to be a rare occurrence, but autopsy series have shown the true overall incidence to be up to 8%. In fact, while the incidence of meningeal metastasis from other malignancies has decreased, the opposite is true of breast cancer, in which clinical evidence suggests an increasing incidence.

Inclusion Criteria:

• Adult (18 years or older) patients, with invasive breast cancer, of all racial and ethnic origins
• Undergoing lumbar puncture for clinical or radiographic suspicion of leptomeningeal metastasis
• Provide study-specific informed consent
• Patients with unequivocal or suspicious MRI findings.
• Of those with a definitive diagnosis of LM (i.e. positive CSF cytology), 10 evaluable patients will be accrued.

Exclusion Criteria:

• Prior CSF fluid which identified malignant cells after 10 evaluable patients with positive CSF are accrued.

In order to fulfill the requirement of sharing the data obtained in the research program, a website where the data acquired will be made available to the scientific community. Through this website, colleagues from other research centers will be able to read about the general information of the proposal, including its objectives and aims. The website will be updated on a regular basis (at least quarterly) to include the advances achieved during the research activities and new results obtained from data processing and statistical analysis. Hyperlinks pointing to other web pages with information related to the program will also be available on our website. These hyperlinks will be divided in those with information for patients and those with information for researchers.

"briefly describe what specific individual participant data sets are to be shared (for example, all collected IPD, all IPD that underlie results in a publication)."

"A description of when the IPD and any additional supporting information will become available and for how long, including the start and end dates or period of availability. This may be provided as an absolute date (for example, starting in January 2025) or as a date relative to the time when summary data are published or otherwise made available (for example, starting 6 months after publication)."

"Describe by what access criteria IPD and any additional supporting information will be shared, including with whom, for what types of analyses, and by what mechanism. Information about who will review requests and criteria for reviewing requests may also be provided."

6 months