This research study is for participants diagnosed with leptomeningeal metastasis disease (LMM), a condition where cancer has spread to the fluid and membranes surround the brain and spinal cord. The purpose of this study is to find out whether a consumer Smartwatch can continuously monitor the participant's health and detect early signs of neurological decline and whether sending an automatic alert to the participant's doctor when a change is detected can help reduce the number of participant hospitalizations.

LMM is a condition where cancer has spread to the fluid and membranes surrounding the brain and spinal cord. It is a common complication of cancer and affects about 5-15% of all cancer patients. It causes rapid neurological decline and survival is usually around 6-12 months. LMM is treated with chemotherapy radiation, but this does not improve neurological function or quality of life. Many of the current assessments for LMM are not good detecting progression and symptoms are often missed.

There will be two parts to this study. Smartwatches will be used to continuously capture data such as gait stability, heart rate variability (HRV), step count, and sleep, which are affected by LMM. The first part of this study is to learn whether this can help detect early signs of neurological decline. The second part of this study will test whether sending an automatic alert to the participant's doctor when a change is detected can help reduce the amount of times the participants are admitted to the hospital unexpectedly.

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.

Data will only be shared in aggregate statistics. There is no universal standard for "raw" wearable data, making IPD sharing less useful without providing the entire technical infrastructure used by the original team. This trial is expected to generate massive datasets (gigabytes per participant). Curating, de-identifying, and hosting this volume of IPD for public access requires significant long-term funding and technical oversight that may be beyond the scope of this Investigator-Initiated Trial (IIT).