Herceptin, generically known as trastuzumab, is a targeted therapy medication used in the treatment of certain types of breast cancer and stomach cancer. Specifically, it is designed for cancers that exhibit an overexpression of the HER2 protein, a condition found in a subset of cancer patients that can lead to aggressive tumor growth. Herceptin works by attaching itself to the HER2 receptors on the surface of cancer cells, thereby inhibiting their ability to receive growth signals and helping the immune system to destroy them. It is often used in combination with chemotherapy or other medications in a treatment regimen. Since its approval, Herceptin has significantly improved the prognosis for HER2-positive cancer patients, offering a tailored approach that targets the cancer's specific genetic makeup.