DS8201a and Pembrolizumab in Participants With Locally Advanced/Metastatic Breast or Non-Small Cell Lung Cancer

To join this study, you must be at least 18 years old and have either advanced breast cancer or advanced non-small cell lung cancer that has spread. Your cancer needs to have a certain characteristic called 'HER2-expressing' or 'HER2-mutant'. This means your cancer cells show a specific protein or a change in their genetic makeup.

You also need to be generally well enough to take part, meaning you can perform your usual daily activities with little difficulty. Your heart and other main organs should be healthy enough to handle the treatment. Additionally, you must be willing to provide a small sample of your tumor tissue before and during the study for testing.

Specific criteria apply depending on which part of the study you might join. For example, some breast cancer patients must have already received a particular treatment called T-DM1 and seen their cancer progress, while others with 'HER2-low' breast cancer must have tried other standard treatments without success. For lung cancer, you must not have received certain types of prior treatments for your HER2-related cancer.

If you decide to join this study, you will receive the study drugs, Trastuzumab deruxtecan and Pembrolizumab, through a drip into your vein. This will happen on the first day of every three-week cycle. The study involves regular visits to the clinic for these treatments and to have various assessments.

These assessments will include physical examinations, blood tests to check your overall health and how your body is handling the drugs, and scans (like CT or MRI) to see how your cancer is responding. You will also need to provide tumor biopsy samples at the start of the study and while you are receiving treatment. The study will continue for as long as the treatment is helping you and you are not experiencing severe side effects. After stopping the treatment, you will have follow-up appointments to monitor your health.