How can breast cancer change from HER2+ to triple negative after treatment?

Cancer cells can sometimes change their characteristics during treatment, which is why doctors often retest tissue when cancer spreads or returns. This kind of change in receptor status can happen, though it's important to have your medical team explain exactly what your recent test results mean for your specific situation. Many others in this community have navigated similar questions about changing diagnoses, and it's completely understandable to feel confused when facing this complexity.