ctDNA (Circulating Tumor DNA)

**What it means:** Tumors shed tiny fragments of their DNA into the bloodstream — this is "circulating tumor DNA." By measuring ctDNA levels in a blood draw (a "liquid biopsy"), doctors can track cancer without doing tissue biopsies. **Why "ctDNA decreases" matters:** When a CDK2 inhibitor causes ctDNA levels to drop, it's a sign that the drug is actively killing tumor cells (since fewer tumor fragments are circulating). This is encouraging early evidence that AVZO-021 is actually hitting its target in real patients, even in a small Phase 1/2 study.