Evaluation of Circulating Tumor Cells (CTC) Relevance in Breast Cancer Follow-up Using the ScreenCell Device

This study is evaluating whether circulating tumor cells (CTCs) — cancer cells shed into the bloodstream — can serve as a useful biomarker to monitor breast cancer treatment response and disease progression over time. **You may be eligible if...** - You are 18 or older - You have been diagnosed with either metastatic breast cancer (cancer that has spread) or non-metastatic invasive breast cancer with no prior treatment - OR you are a healthy volunteer with no current cancer diagnosis and a recent normal mammogram within the past year **You may NOT be eligible if...** - You are under 18 - You are pregnant or breastfeeding - A new cancer (other than breast cancer) is detected during the study - (For healthy volunteers): You have a history of any cancer - (For breast cancer patients): No circulating tumor cells are detected during the screening phase Talk to your doctor to see if this trial is right for you.