Study of 68Ga-R10602

This study tests a new PET imaging agent called 68Ga-R10602, which attaches to estrogen receptors in tumor cells, to better visualize breast cancer spread in the body. It is being studied in women with hormone receptor-positive (ER/PR-positive) breast cancer that has returned or spread. **You may be eligible if...** - You are 18 or older - You have confirmed hormone receptor-positive (ER and/or PR-positive) metastatic or advanced breast cancer - Your cancer has progressed on at least one line of prior endocrine (hormone-blocking) therapy - You have at least one measurable lesion visible on imaging - Your liver and kidney function are adequate **You may NOT be eligible if...** - You have received radiation or another radioactive agent within a short time before the scan - You had major surgery within the past 21 days - You have severe uncontrolled heart disease (heart failure, uncontrolled arrhythmia, or recent heart attack) - You have a recent stroke or active serious infection - You have HIV, active hepatitis B or C - You are pregnant or nursing Talk to your doctor to see if this trial is right for you.