tucatinib

This study is being done to find out if tucatinib with other cancer drugs works better than standard of care to treat participants with HER2 positive colorectal cancer. This study will also determine what side effects happen when participants take this combination of drugs. A side effect is anything a drug does to the body besides treating your disease. Participants in this study have colorectal cancer that has spread through the body (metastatic) and/or cannot be removed with surgery (unresectable). Participants will be assigned randomly to the tucatinib group or standard of care group. The tucatinib group will get tucatinib, trastuzumab, and mFOLFOX6. The standard of care group will get either: * mFOLFOX6 alone, * mFOLFOX6 with bevacizumab, or * mFOLFOX6 with cetuximab mFOLFOX6 is a combination of multiple drugs. All of the drugs given in this study are used to treat this type of cancer.

This clinical trial is studying solid tumor cancers. A solid tumor is one that starts in part of your body like your lungs or liver instead of your blood. Once they've grown bigger in one spot or spread to other parts of the body, they're harder to treat. This is called advanced or metastatic cancer. Participants in this study must have breast cancer or gastric cancer. Participants must have tumors that have HER2 on them. This allows the cancer to grow more quickly or spread faster. There are few treatment options for patients with advanced or metastatic solid tumors that express HER2. This clinical trial uses an experimental drug called disitamab vedotin (DV). Disitamab vedotin is a type of antibody drug conjugate or ADC. ADCs are designed to stick to cancer cells and kill them. This clinical trial uses a drug called tucatinib, which has been approved to treat cancer in the United States and some other countries. This drug is sold under the brand name TUKYSA®. This study will test how safe and how well DV with tucatinib works for participants with solid tumors. This study will also test what side effects happen when participants take these drugs. A side effect is anything a drug does to the body besides treating the disease.