Epratuzumab and Rituximab in Treating Patients With Previously Untreated Follicular Non-Hodgkin Lymphoma

DISEASE CHARACTERISTICS: * Histologically\* confirmed follicular non-Hodgkin lymphoma (NHL) * Previously untreated disease * WHO classification grade 1, 2, or 3a (\> 15 centroblasts per high power field with centrocytes present) that is stage III, IV, or bulky (i.e., single mass ≥ 7 cm in any unidimensional measurement) stage II disease NOTE: \*Bone marrow biopsies as the sole means of diagnosis are not acceptable, but they may be submitted in conjunction with nodal biopsies; fine-needle aspirates are not acceptable for diagnosis * Confirmed CD20 antigen expression by flow cytometry or immunohistochemistry * Measurable disease by physical examination or imaging studies * Any tumor mass \> 1 cm is acceptable * No nonmeasurable disease only, including any of the following: * Bone lesions * Ascites * Pleural/pericardial effusion * Lymphangitis cutis/pulmonis * Bone marrow (involvement by NHL should be noted) * No known CNS involvement by lymphoma * Required to participate in companion FDG-PET imaging study CALGB 580701 PATIENT CHARACTERISTICS: * ECOG performance status ≤ 2 * Absolute neutrophil count ≥ 1,000/μL * Platelet count ≥ 50,000/μL * Patients with HIV infection are eligible provided they meet the following criteria: * No evidence of coinfection with hepatitis B or C * CD4+ cell count ≥ 400/mm\^3 * No evidence of resistant strains of HIV * If not on anti-HIV therapy, HIV viral load \< 10,000 copies HIV RNA/mL * If on anti-HIV therapy, HIV viral load \< 50 copies HIV RNA/mL * No history of AIDS-defining conditions * Not pregnant or nursing * Fertile patients must use effective contraception during and for 3 months after completion of study therapy * No known Human Anti-Chimeric Antibody (HACA)-positivity PRIOR CONCURRENT THERAPY: * No prior therapy for NHL including chemotherapy, radiotherapy, or immunotherapy (e.g., monoclonal antibody-based therapy) * More than 2 weeks since prior corticosteroids except for maintenance therapy for non-malignant disease * No concurrent dexamethasone or other steroids as antiemetics except for the following circumstances: * Treatment of acute infusion reactions according to institutional procedures * No concurrent hormonal therapy except steroids for adrenal failure OR hormones for non-disease-related conditions (e.g., insulin for diabetes) * No other concurrent chemotherapeutic agents