Oncologic Biomarker Context for MHS

**What it means:** A biomarker is a measurable biological indicator. In cancer, biomarkers (like ctDNA, tumor size on imaging, or protein levels in blood) tell doctors how the cancer is responding to treatment. **Parallel for MHS:** Developing biomarkers for MHS is one of the biggest challenges. Unlike cancer (where tumor size is measurable), MHS symptoms are behavioral and cognitive — much harder to quantify. The natural history studies are trying to identify which measures (eye-tracking, EEG, behavioral scales, etc.) work best as "biomarkers" for MHS progression. This is why the Boston Children's and Volare studies are so important — they're building the toolkit of reliable measures that future treatment trials will need.