Treatments for B cell cancers that return or are hard to treat often do not last long. Even when patients improve at first, the cancer usually comes back. Drugs called Bruton’s tyrosine kinase (BTK) inhibitors have helped people with conditions such as chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), mantle cell lymphoma (MCL), Waldenström’s macroglobulinemia (WM), marginal zone lymphoma (MZL), and follicular lymphoma (FL). However, these drugs cannot fully stop the disease, because cancer cells can change and resist treatment. This study is testing BGB...