Targeted cancer therapies are designed to exploit specific molecular markers or pathways that are overexpressed or mutated in cancer cells. However, many of these targets are not exclusive to cancer cells and can be present in normal tissues. When a drug binds to these targets in healthy cells, it can disrupt normal cellular functions, leading to toxicity. For instance, HER2 is a well-known target in breast cancer, but it is also expressed in other tissues like the heart, leading to cardiotoxicity when targeted by certain therapies.
