The study is for adults with advanced extrapulmonary neuroendocrine cancer (epNEC), which is a type of cancer that starts in hormone-producing cells outside the lungs. The study tests a combination of a new drug called obrixtamig with standard chemotherapy drugs, carboplatin and etoposide, to see if it helps patients live longer compared to just using the standard chemotherapy. Obrixtamig is like an antibody, a part of the immune system that helps fight diseases.

Participants are split into two groups by chance: one group gets obrixtamig with chemotherapy, followed by obrixtamig alone for up to 3 years. The other group gets only the standard chemotherapy for about 4 months. Treatments are given through a vein infusion. Doctors check participants' health regularly and measure tumor sizes to see if the treatment is effective.

• Participants visit the study site regularly; some may stay overnight for initial treatments.
• Eligible adults need to have specific tumor characteristics and should not have had previous similar treatments.
• The study involves monitoring for side effects and requires tumor tissue samples for analysis.