Investigation of Drug-drug Interaction of Ritonavir and Itraconazole on the Pharmacokinetics of SHR-A1811 in Subjects With HER2-expressing Advanced Breast Cancer

This study examines how two common medications (ritonavir and itraconazole) affect the levels of a cancer drug called SHR-A1811 in the body. It is enrolling women with HER2-expressing advanced breast cancer to understand potential drug interactions. **You may be eligible if...** - You have advanced breast cancer that tests positive for HER2 - You are in good general health (able to carry out normal activities) - Your blood counts, liver function, kidney function, and heart function meet the study requirements - Your expected survival is at least 3 months **You may NOT be eligible if...** - You have uncontrolled infections or serious other illnesses - Your organ function tests fall outside acceptable ranges - You have significant heart problems (low heart pumping function) Talk to your doctor to see if this trial is right for you.