A Study for CTC Expression and cfDNA/RNA Assessment in Metastatic Breast Cancer Patients

This study collects blood samples from people with advanced or metastatic breast cancer to test for circulating tumor cells and bits of tumor DNA/RNA floating in the bloodstream. Researchers want to learn whether these tests can help predict how well treatments are working. **You may be eligible if...** - You are over 18 years old - You have invasive breast cancer that has spread and cannot be surgically removed - You have hormone receptor-positive, HER2-negative, or triple-negative breast cancer starting first-line therapy or later - Or you have HER2-positive breast cancer starting second-line therapy or later - Your doctor has already ordered circulating tumor cell and cfDNA/RNA tests as part of your routine care **You may NOT be eligible if...** - You are pregnant - Your doctor determines you are unable to safely provide blood samples Talk to your doctor to see if this trial is right for you.