This study is testing a drug called loncastuximab tesirine to see if it helps people with a type of immune cell cancer called Marginal Zone Lymphoma (MZL). MZL is a cancer that affects certain white blood cells in the immune system. Researchers want to understand the good and bad effects of this drug on patients. Only people 18 or older with confirmed MZL and who meet specific health criteria can join. Participants must have tried other treatments before. The study excludes those with other cancers or health problems like heart failure or infections. Participants must avoid pregnancy or fathering children during and for a time after the study.

• The study involves taking the drug and regular health check-ups.
• Participants may face side effects, but researchers will monitor and manage them.
• It's important to discuss with your doctor if this study fits your health needs.