Umbralisib and Rituximab as Initial Therapy for Patients With Follicular Lymphoma and Marginal Zone Lymphoma

Inclusion Criteria: * Participants must have histologically confirmed follicular lymphoma grade 1-3A or marginal zone lymphoma by WHO criteria. * Participants must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter \[LDi\] to be recorded for non-nodal lesions and short axis for nodal lesions) as ≥15 mm in LDi for nodal disease or \>10 mm in LDi for extranodal lesions. * Requires therapy based on: symptomatic disease, threatened end-organ dysfunction, compressive disease, cytopenias secondary to lymphoma, bulky disease (defined as any site ≥7 cm, or 3 or more sites ≥3cm), or steady progression. * For patients with follicular lymphoma: No prior systemic therapy for follicular lymphoma. Prior radiation to a single site of disease is allowed if completed at least 2 weeks prior to initiation of protocol therapy and there are additional sites of measurable disease outside of the radiation field. * For patients with marginal zone lymphoma: No prior systemic therapy for marginal zone lymphoma. Prior radiation or surgical resection is allowed if there are additional sites of measurable disease outside of the radiation field. Prior radiation must be completed at least 2 weeks prior to initiation of protocol therapy. Prior H. pylori eradication therapy is allowed. * Age \>18 years. * ECOG performance status ≤2 * Participants must have adequate organ function as defined below: * total bilirubin \<1.5 x i…