This study is being done to understand how to treat Mantle Cell Lymphoma (MCL). The goals of treatment are to control the lymphoma with the least amount of side effects. In many cases, MCL is treated with an antibody plus chemotherapy. An antibody is a laboratory-produced substance created to attach to proteins on the cancer cells, eventually destroying them. Chemotherapy is medicine that specifically destroys cancer cells.

The purpose of this study is to find out what effects, good and/or bad, the drugs Ofatumumab and Bendamustine have on this type of cancer. Patients in this study will either receive Ofatumumab alone, or Ofatumumab combined with Bendamustine.

Inclusion Criteria:

• Untreated, non-transplant eligible, newly diagnosed mantle cell lymphoma with measurable disease as determined by CT, and bone marrow biopsy.
• Age > or = to 65 years or > 18 year and ineligible for HDT/ASCT.
• Subjects must not be candidates for intensive high-dose chemotherapy, with or without an autologous stem cell transplant (ASCT), due to one or more of the following factors:
• Age ≥ 65 years
• Patients <65 years of age must be ineligible for HDT/ASCT on the basis of comorbidity, organ dysfunction or patient refusal for HDT/ASCT Comorbid disease, such as CAD, CHF, pulmonary dysfunction, liver or kidney dysfunction, precluding high dose therapy secondary to expected increased morbidity and mortality.
• poor performance status (KPS 70% or less)
• Ejection fraction <45%
• Impaired pulmonary function test with DLCO <50% expected
• Patient refusal
• Medical conditions which in the opinion of the treating physician and DMT preclude HDT/ASCT.
• Patients must have a serum creatinine clearance ≥ 40 mL/min (as per the Jelliffe method) or by 12-hour or 24-hour urine creatinine clearance.
• Patients must have ANC>1,000/mcl and Platelets>100,000/mcl (unless secondary to MCL).
• Patients must have a bilirubin level of < 2.0 mg/dl in the absence of a history of Gilbert's disease (or pattern consistent with Gilbert's).
• Negative serologies for Hepatitis B (HB) defined as a negative test for HBsAg. In addition, if negative for HBsAg but HBcAb positive (regardless of HBsAb status), a HB DNA test will be performed and if negative, patient may be included but must undergo HBV DNA PCR testing at the beginning of treatment and throughout treatment duration, at least every 2 months. In addition patients will require treatment with Entacavir .5mg po qday per MSKCC institutional guidelines.
• No active co-morbid cardiac condition such as active CHF or CAD.
• KPS performance ≥ 70%.
• Histologically confirmed mantle cell lymphoma classified according to WHO criteria confirmed at MSKCC.
• No prior treatment for mantle cell lymphoma with the exception of corticosteroids for 7 days or less or 1 course of involved-field radiation.
• No prior malignancies within 5 yrs, unless treated early stage breast cancer, treated carcinoma in situ of the cervix, resected skin malignancies, or treated prostate cancer.
• Women who are pre-menopausal must have a negative serum pregnancy test. Subjects must agree to use appropriate contraception until 4 weeks after the completion of chemotherapy.
• Patients must be HIV negative, and have negative serologies for Hepatitis C.

Exclusion Criteria:

• Subjects who have current active hepatic or biliary disease (with exception of patients with Gilbert's syndrome, asymptomatic gallstones, hepatic involvement by MCL, or stable chronic liver disease per investigator assessment).
• Known pregnancy or breast-feeding.
• Medical illness unrelated to MCL within the prior one month that will preclude administration of chemotherapy safely. This includes patients with uncontrolled infection, chronic renal insufficiency, myocardial infarction within the past 6 months, unstable angina, active congestive heart failure, cardiac arrhythmias other than chronic atrial fibrillation and chronic active or persistent hepatitis.