Inclusion Criteria:

• Age >= 18

• Prior tissue diagnosis of breast cancer

• Confirmed diagnosis of leptomeningeal metastases (LM) with positive cerebrospinal fluid (CSF) cytology for malignancy and meningeal enhancement (type 1A, 1B, and 1C)

• Radiographic evidence on MRI of leptomeningeal enhancement within the cervical, thoracic or lumbar spine on spinal MRI

• Life expectancy of at least 6 weeks

• Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, 2, or 3

• Recovery from any neurotoxic effects of prior therapy

• Platelet count greater than 25 x 10^9/L

• Absolute neutrophil count (ANC) greater than 0.5 x 10^9/L

• Patients must have adequate liver function, total bilirubin < 2.5 mg/dL, unless elevated total bilirubin is due to elevated indirect bilirubin from known Gilbert's disease, aspartate aminotransferase (AST) =< 3.5 times upper limits of normal; adequate renal function [calculated estimated glomerular filtration rate (eGFR) >= 30 mL/min/ body surface area (BSA)]

• Patients or legal medical representative must provide written informed consent

• Patients must have suitable body habitus for placement of transducer arrays

• Patients must be willing to wear the device for at least 18 hours a day (averaged over monthly)

• Patients must be willing to return for the scheduled evaluations and perform the required assessments

• Patients are without other disease or situation which would significantly compromise adequate assessment of safety and feasibility of the TTF

• Patient willing to start a study treatment with TTF =< 14 days from registration

Exclusion Criteria:

• Concomitant therapy:

  • Must not be receiving concurrent high-dose methotrexate (>= 3 g/m^2), high dose thiotepa, or high-dose cytarabine (>= 3 g/m^2). Any other systemic chemotherapy, targeted treatment, hormonal or immunotherapy directed at the primary systemic malignancy is permitted

  • Must not have received radiation therapy (RT) to the brain or spinal cord within 2 weeks of initiation of TTF

  • Must be at least 1 week from cessation of any prior intrathecal chemotherapy

• Women of childbearing age who are pregnant or lactating. (Male and female patients who are fertile must be willing to use an effective means of birth control to avoid pregnancy)

• Patients with uncontrolled or untreated infection including active hepatitis, and human immunodeficiency virus (HIV)

• Patients receiving any other investigational agents and must not have received any other investigational agent within 14 days prior to registration. The 14-day period should be extended if the investigational agent is known to have delayed toxicity

• Patients known to be allergic to the hydrophilic gel utilized for transducer attachment

• Patients with surgical hardware within the planned area of treatment in the spine (e.g., titanium rods, screws, fixation devices)

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 08/12/2025. Questions regarding updates should be directed to the study team contact.