Final answer:
The purpose of lansoprazole for a patient with a brain tumor is gastric acid reduction.
Step-by-step explanation:
The purpose of lansoprazole (Prevacid) for a patient with a brain tumor is c) Gastric acid reduction. Lansoprazole belongs to a class of medications called proton pump inhibitors (PPIs), which work by reducing the production of stomach acid. While lansoprazole is primarily used to treat conditions such as gastroesophageal reflux disease (GERD) and stomach ulcers, it may also be prescribed to patients with brain tumors to reduce the risk of gastrointestinal side effects caused by other medications or treatments.