Follicular lymphoma (FL) is the most common indolent lymphoma diagnosed in the United States.1 With approximately 14,000 cases per year, it accounts for about 35% of all non‐Hodgkin lymphomas (NHLs) and 70% of indolent lymphomas.2-4 While still considered an incurable disease, improvements in diagnosis and therapeutic advances have improved outcomes. The development of anthracycline-containing chemotherapy and use of the anti-CD20 monoclonal antibody rituximab, along with the newer phosophatidylinositol-2-kinase-delta (PI3Kδ) inhibitors (idelalisib, copanlisib, and duvelisib), have steadily extended survival.5,6 The median survival is now close to 20 years.

The mortality rate for patients with FL remains at 0.5 per 100,000 persons (2013-2017 cases and deaths)and the clinical heterogeneity of the disease is still poorly understood.7 FL can remain indolent for decades in some patients while in others it will follow an aggressive clinical course. Approximately 10% to 15% of patients with FL will experience an aggressive disease trajectory with a shortened lifespan, while others with an indolent course may survive for decades with minimal impact on their lives.8 Most patients, however, will experience a pattern of relapse and remission and require numerous lines of treatments throughout their lifetime. Early recurrence following frontline chemoimmunotherapy consistently occurs in 20% of all patients, and has emerged as a predictor of poor survival.9

FL is defined as a lymphoma of follicle center B-cells, which typically manifest with follicular pattern and originates in the lymph nodes.10 Many adult patients will initially present with asymptomatic lymphadenopathy, which can fluctuate for years, and at least 70% will have bone marrow involvement. This reflects stage IV disease at diagnosis but variability in tumor burden can be significant.8 The involvement of other organs is uncommon, although a rare extranodal variant of FL can present in the intestines. Involvement of the gastrointestinal tract tends to follow a particularly indolent course with a much better prognosis.11

About 90% of FL cases are characterized by the recurrent chromosomal translocation t(14;18)(q32;q21), which results in the influence of IgH promoter on BCL2, ultimately leading to the overexpression of the antiapoptotic BCL2 protein in cells of the FL microenvironment.12 FL is also associated with a characteristic immunophenotype that includes CD20+, CD10+, BCL2+, CD23+/-, CD43-, CD5-, CCND1-, and BCL6+, while cases may occasionally be CD10- or BCL2-.13 Aggressive disease can result in the histologic transformation of FL to diffuse large B cell lymphoma (DLBCL), which occurs in 15% of patients with a risk of 2% to 3% per year, and is associated with a poor prognosis. Transformation is often associated with rapid progression of lymphadenopathy, extranodal disease aside from bone marrow, systemic symptoms, hypercalcemia, elevated serum lactate dehydrogenase (LDH), and a limited response to initial therapy.14 MYC abnormalities are also associated with transformation to a clinically aggressive and chemorefractory disease state, and other genetic aberrations associated with a poor prognosis include 1p36 deletions (usually in association with mutations of TNFRSF14), TP53 mutations, MLL2 and EZH2 mutations, and CDKN2A deletions.8

Risk Stratification

Defining a patient’s individual risk can be difficult due to the significant biologic heterogeneity in FL at the histologic, genetic, epigenetic, and proteomic levels. Tools and models have been developed to help inform treatment decisions and to allow clinicians to evaluate individual patient risk. One model is the FL international prognostic index (FLIPI), which was developed to stratify patients by risk and to predict survival (Table). FLIPI has been validated as a diagnostic model for patients treated in both the pre- and post-rituximab eras.15 The endpoint of the model is overall survival, and 5 parameters are used: age (>60 vs ≤60), serum LDH level (>upper limit of normal [UPLN] vs ≤UPLN), number of nodal areas (>4 vs ≤4), hemoglobin level (<120 vs ≥120g/L) and Ann Arbor state (III-IV vs I-II). Three risk groups were identified: low, intermediate and high.

The National LymphoCare Study (NLCS), a prospective, observational cohort study, which collects data on FL patients treated in community practices, evaluated the FLIPI in the era of routine first-line rituximab (R) and R-chemotherapy regimens.15 The results showed that it was able to predict distinct outcomes for both overall and progression-free survival (PFS), and that it remained a valid and important prognostic tool for patients receiving contemporary immunochemotherapy regimens.

An updated model, the FLIPI2, was designed to evaluate newly diagnosed patients treated with contemporary therapies, and it also incorporated PFS as an endpoint. The final prognostic model included age, hemoglobin levels, longest diameter of largest involved lymph node, β2-microglobulin levels, and bone marrow involvement, and it was shown to be highly predictive of treatment outcomes. It also stratified patients into 3 distinct risk groups with 3-year PFS rates ranging from 51% to 91%, and 3-year overall survival rates ranging from 82% to 99%.16

A higher FLIPI score may suggest that treatment should be initiated rather than a “watch and wait” approach, but other factors need to be determined when assessing risk, including tumor burden. There are various criteria that are used to evaluate tumor burden, such as the Groupe d’Etude des Lymphomes Folliculaires (GELF).17 Data show that a high tumor burden, as defined by GELF criteria, was associated with worse overall survival and PFS in patients treated with first-line R plus chemotherapy.18

The World Health Organization has also classified FL into grade 1, grade 2, and grade 3, which has been further divided into grades 3a and 3b. Grade 3a is indicated by the presence of centrocytes, while grade 3b is indicated by the presence of sheets of centroblasts. Because grade 3b is clinically and biologically similar to DLBCL, it is also treated similarly.19

First-Line Treatment

Less than 10% of patients present with stage I/II disease, and most will have disseminated disease at diagnosis.13,19 Guidelines from the National Comprehensive Cancer Network (NCCN) only offer treatment recommendations for FL grade 1-2 and consider grade 3a to be an “area of controversy.”13 In addition, the NCCN guidelines noted that grade 3b FL is commonly treated as DLBCL.

The preferred first-line therapy is chemotherapy in combination with an anti-CD20 antibody such as rituximab. These combinations include bendamustine plus rituximab; rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP); or rituximab, cyclophosphamide, vincristine, and prednisone (R-CVP). The NCCN also recommends rituximab as monotherapy or combined with immunomodulator lenalidomide.13 An update of the FOLL05 trial ( Identifier: NCT00774826) showed that among patients with advanced FL, treatment with R-CVP, R-CHOP, or rituximab plus fludarabine and mitoxantrone resulted in similar 8-year overall survival; however toxicity profiles varied.20 Compared with patients who received R-CHOP, patients who were initially treated with R-CVP had a higher risk for lymphoma progression and risk of requiring additional therapy. Of the 3 regimens, the investigators of the study suggested that R-CHOP should be the preferred option.

Combination rituximab plus lenalidomide represents a nonchemotherapy option for patients, and results of the RELEVANCE trial ( Identifier: NCT01476787) found it comparable to standard regimens.21 The phase 3 superiority trial compared rituximab plus lenalidomide with rituximab plus chemotherapy in treatment-naive patients and demonstrated that overall response rate (ORR) was comparable between groups. The 3-year PFS was 77% and 78% for rituximab plus lenalidomide and immunochemotherapy arms. A higher rate of grade 3 and 4 neutropenia (32% vs 50%) and febrile neutropenia (2% vs 7%) was observed in the chemotherapy group.

Extended dosing or consolidation with rituximab is an option for patients initially presenting with high tumor burden, and radioimmunotherapy can also be given following induction with chemotherapy or chemoimmunotherapy.13 Studies have reported a benefit with extended dosing including data from the phase 3 ECOG (E1496) study which showed a PFS benefit with rituximab maintenance in patients with advanced indolent lymphoma who had responded to first-line CVP regimen.22 The subgroup of FL patients who received maintenance therapy had a PFS of 64% vs 33% for those who didn’t. However, the 3-year overall survival rate did not significantly differ between groups (91% vs 86%, respectively).

Long term follow-up results of the PRIMA study ( Identifier: NCT00140582) also demonstrated a benefit for extended therapy. Patients treated with rituximab maintenance had a median PFS of 10.49 years compared with 4.06 years for those who did not (P =.0001).23 However, no differences were seen in projected median overall survival, and in patients with a low tumor burden, the RESORT study ( Identifier: NCT00075946) showed similar results to rituximab maintenance and rituximab retreatment at the time of relapse.24

Transformation to Aggressive Lymphoma

Histological transformation of FL to an aggressive lymphoma will have a substantial effect on outcomes, and in the era before immunochemotherapy regimens, the risk was relatively high at 28% at 10 years.25 A more recent analysis showed that the inclusion of rituximab into first-line therapy has significantly reduced the risk of transformation to 7.7%.26 Advanced-stage and high-risk FLIPI and International Prognostic Index (IPI) scores at diagnosis correlate with a higher risk for histological transformation.

A subset of patients with indolent disease may be able to be cured by high-dose chemotherapy followed by autologous hematopoietic cell transplantation (ASCT), although it is unclear whether ASCT is preferable to immunochemotherapy.27 Some data suggest that ASCT following chemoimmunotherapy may improve outcomes as opposed to chemoimmunotherapy alone, with 5-year survival rates of 55% compared with 40%.28 However, other data showed better outcomes following R-CHOP without ASCT, with 5-year overall survival rates of 64.3%.29

Relapsed/Refractory Disease

Relapse is part of the disease trajectory in FL, but many treatment options are now available. Patients with relapsed or progressive disease following first-line therapy can sometimes benefit from a second period of observation, depending on individual characteristics including GELF criteria, presence of significant cytopenia secondary to lymphoma, bulky disease, splenomegaly, and experiencing steady disease progression over at least 6 months.

For second-line and subsequent therapy, NCCN guidelines recommend chemoimmunotherapy as per first-line therapy, rituximab alone; lenalidomide plus rituximab; radioimmunotherapy; idelalisib; fludarabine plus rituximab; and rituximab, fludarabine, mitoxantrone, and dexamethasone.13 Some patients may be treated according to the guidelines for DLBCL, depending on individual characteristics.

For second-line consolidation or extended dosing, the NCCN recommends rituximab maintenance, or high-dose therapy with autologous stem cell rescue or allogeneic stem cell transplant for highly selected patients.13

About a quarter of patients will be refractory to first-line immunochemotherapy and/or experience disease progression within the first 24 months. Early progression is associated with a poorer survival, as demonstrated by a combined analysis of 3 CALGB clinical trials, which showed an association with an increased risk of death.30 Those with early progression had a 2-year overall survival of 80% and 5-year overall survival of 74% compared to 99% and 90% for patients without early progression. Thus, disease progression within 24 months of remission is a prognostic marker for overall survival in patients treated with rituximab-containing immunotherapy.

The PI3Kδ inhibitors are a newer addition to the armamentarium for treating relapsed/refractory disease after 2 prior therapies and both idelalisib and copanlisib have demonstrated efficacy in a high-risk population with disease relapse less than or equal to 2 years after first-line therapy.31-35 A phase 2 trial comprised of 125 patients with rituximab- and alkylating agent–refractory indolent NHL (including 72 patients with FL) showed that treatment with idelalisib resulted in tumor reductions in 90% of the cohort, with an ORR of 57% (6% complete responses).31 A post hoc subgroup analysis of the 72 patients with FL showed an ORR of 55.6% (13.9% complete and 41.2% partial response) and the overall disease control rate was 87.5%.36

The phase 2 CHRONOS-1 ( Identifier: NCT01660451) found that treatment with copanlisib in patients with relapsed/refractory indolent NHL after 2 or more prior lines of therapy resulted in an ORR of 58.7% in the subgroup of 104 patients with FL (20.2% complete response and 38.5% partial response).35 Median duration of response was 12 months. Duvelisib was evaluated in the phase 2 DYNAMO study ( Identifier: NCT01882803) that included 129 patients with indolent NHL refractory to both rituximab and chemotherapy or radioimmunotherapy.33 The ORR was 47.3% (42.2% for the subgroup with FL), and estimated median duration of response and median PFS were 10 and 9.5 months, respectively.

The use of either allogeneic or ASCT in FL has also been studied in numerous clinical trials, but a consensus on its use has not yet been established.37 Numerous phase 2 studies conducted before the introduction of rituximab found that about that about 40% of patients with good performance status and chemosensitive relapsed disease could experience prolonged PFS and overall survival following high-dose therapy and ASCT.38,39 More recently, studies have looked at the use of ASCT for high-risk patients with early relapse, with 1 reporting a 5-year overall survival rate of 70% following ASCT in this patient population.40 Other results from research conducted by the Center for International Blood and Marrow Transplant Research and the National LymphoCare Study, suggests ASCT in this population was associated with a higher 5-year overall survival as compared to patients without ASCT (73% vs 60%).41

Treatment with CD19 CAR-T cells is an emerging and promising therapeutic option for patients with FL, and there are currently 2 US Food and Drug Administration-approved products for patients with FL that is relapsed/refractory after 2 prior therapies: tisagenlecleucel and axicabtagene ciloleucel. One study reported a 71% response rate in 14 patients, and at a median follow-up of 28.6 months, 89% of the responders remained progression free.42 In another study, the rate of complete remission was 88%, and sustained remissions were achieved.43

Current first-line regimens for FL typically achieve high response rates, but for the most part, patients will be treated with multiple lines of therapies and/or different modalities throughout their lifetime. The outcome of these different regimens and their effect on patient survival are evolving, as new therapies come on the market and research continues into the underlying mechanisms of the disease.


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Reviewed October 2020