Ixazomib Citrate and Rituximab in Treating Patients With Indolent B-cell Non-Hodgkin Lymphoma

OUTLINE: Patients receive ixazomib citrate orally (PO) on days 1, 8 ,15, and 22. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity. Upon completion of 6 cycles of ixazomib citrate therapy, patients also receive rituximab intravenously (IV) once weekly for 4 doses total, followed by ixazomib citrate alone, until disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30 days and then every 3 months for 3 years.