Wearable-Triggered Digital Safety Net for Real-Time Monitoring & Intervention in Leptomeningeal Metastasis

Inclusion Criteria: * Participants must have leptomeningeal metastasis (LMM) diagnosed per clinical, imaging, and/or CSF/cytology criteria (cytology, flow cytometry, or circulating tumor DNA), arising from any solid or hematologic tumor primary. * Participants must be undergoing active anti-cancer therapy (systemic, intrathecal, and/or radiation) or active surveillance for LMM. * Age ≥18 years at the time of study enrollment. Because no safety or dosing data are available for wearable monitoring studies in children with LMM, participants under 18 years of age are excluded. * Karnofsky Performance Status (KPS) ≥50 at time of study enrollment \[See Appendix I\], to ensure feasibility of wearing the device for ≥10 hours/day. * Participants must have access to a compatible smartphone: * iPhone running iOS 16 or higher and willingness to wear Apple Watch ≥10 hours/day; OR * Android smartphone compatible with the study application and willingness to wear Samsung Galaxy Watch ≥10 hours/day. * Ability to provide informed consent (or a legally authorized representative \[LAR\] is available and willing to provide consent on the participant's behalf, if appropriate). Exclusion Criteria: * Anticipated life expectancy \<4 weeks at time of screening, per the treating physician. * Severe dermatologic or musculoskeletal conditions precluding smartwatch wear (e.g., significant skin conditions on the wrist or forearm where the device will be placed, including tattoos that may substantially interfere with optical sensor function). * Inability to adhere to study procedures after training, as assessed by the study team at enrollment. * No access to a compatible smartphone (participant or caregiver) to interface with the watch application for symptom documentation and data transfer. * Inability to give informed consent due to severe aphasia, severe cognitive impairment, or other language barrier, unless a legally authorized representative is available and willing to participate.