Rituximab and Lenalidomide vs Rituximab Alone as Maintenance After R-chemoterapy for Relapsed/Refractory FL Patients

Among Non-Hodgkin lymphomas (NHL), Follicular Lymphoma (FL) is the second one in terms of frequency, accounting for about 25% of all NHL cases in the western hemisphere. A predominance in females is reported, and the median age at the diagnosis is 60 years.

FL cells originates from normal counterparts germinal B cells. At a molecular level, the pathology is thought to be dependent on multiple DNA alterations. However, a large amount of patients (approximately 85%) have t(14;18), with a consequent overexpression of anti-apoptotic protein BCL-2.

An additional hallmark of pathology is bone marrow involvement (70% of patients), while this is seldom noticed in other organs. Finally, 20% of patients show high levels of serum lactate dehydrogenase (LDH) and/or B symptoms.

FL is actually considered an incurable disease. Although FL responds well to initial chemotherapy, most patients will eventually relapse, requiring multiple subsequent therapeutic regimens during the course of disease to achieve new period of remission, that are nevertheless shorter. Relapsed/refractory FL in advanced stage, especially in older patients, has a relatively poor prognosis, and several patients die for infectious complications and/or progressive disease. This subset of patients usually do not survive more than 5 years.

Thus there is a need for new, less toxic and more active treatment in particular for patients with recurrent disease. The addition of Rituximab to chemotherapy showed a clear benefit in terms of overall response rate, quality of response, event-free survival and, in most studies, overall survival; nevertheless, relapses still occur. Moreover Rituximab also proved highly effective when employed as maintenance treatment either following chemotherapy or Rituximab-supplemented chemotherapy. The success of Rituximab maintenance led to the widespread opinion that in the context of indolent lymphomas novel "smart" drugs characterized by a good safety profile need to be carefully evaluated not only in the induction but also in the maintenance setting.

Autologous stem cell transplantation and radioimmunotherapy are therapeutic option for relapsed/refractory FL patients, but can be considered only for younger or fit patients and can be delivered only in large institutions.

Therefore the search of new, more manageable, therapeutic agents with different mechanisms of action, especially for elderly or frail patients, is ongoing.

Bendamustine is highly effective in relapsed/refractory indolent non-Hodgkin lymphoma (NHL) and Mantle Cell Lymphoma (MCL), including patients who are refractory to rituximab and those previously treated with other alkylating agents. Therefore, bendamustine is now widely used in this setting and provides another effective treatment option for patients who progress after CHOP-R. Two phase II studies have combined bendamustine (90 mg/m2 days 2-3 every 28 days) with rituximab (375 mg/m2 day 1) and both reported similar results. The overall response rate was 90% (60% CR) for the entire patient population, and median Progression-free survival (PFS) for all patients was 24 months. Based on these encouraging results in the relapsed/refractory setting, the Study group indolent Lymphomas (StiL) initiated a large, randomized, phase III trials of bendamustine (90 mg/m2 days 1-2 every 28 days) plus rituximab (375 mg/m2 day 1). This trial compared B-R with standard CHOP-R (21-day cycles) in previously untreated patients with indolent NHL and MCL. 549 patients with predominantly stage IV disease were enrolled, and the treatment groups were well balanced for all baseline characteristics. Approximately 55% of patients had FL, approximately 20% had MCL, and the remaining 25% had other indolent lymphomas. Although the overall response rate was similar in the B-R and CHOP-R arms (93.8% and 93.5%, respectively), the CR rate was significantly higher in the B-R arm (40.1% compared with 30.8% for CHOP-R; P .03), and the median PFS was significantly longer in the B-R arm (54.8 months v 34.8 months for CHOP-R; P .0002). No difference in survival has been observed thus far, further follow-up of this ongoing study will be required to address whether B-R improves survival compared with CHOP-R. Nevertheless, bendamustine plus rituximab yielded more durable responses and improved PFS compared with CHOP-R in previously untreated patients with indolent lymphomas. Moreover, bendamustine plus rituximab was better tolerated.

Lenalidomide is an immunomodulatory agent with multiple mechanisms of action wich include antiproliferative activity as well as microenvironmental effects such as inhibition angiogenesis and stimulation of T-cell mediated response. Lenalidomide given as monotherapy proved to be active, with an acceptable toxicity profile, in B-cell malignancies such as multiple myeloma, chronic lymphocytic leukemia, mantle cell lymphoma and diffuse large B-cell lymphoma.

Recent reports on Lenalidomide in FL, both for untreated and relapsed patients, are promising.

Forty-three patients with relapsed or refractory indolent non Hodgkin's lymphoma (NHL) were treated with oral Lenalidomide 25 mg once daily on days 1 to 21 of every 28-day cycle for 52 weeks or until progression. Twenty-two of the 43 patients enrolled had FL In this subgroup overall response rate was 27%, with a 9% complete remission rate. Most common adverse events were myelosuppression, fatigue, gastrointestinal events and cutaneous rash, while predominant grade 3/4 serious adverse events were neutropenia and thrombocytopenia. Despite a median duration of response longer than 16.5 months, there was a disappointing median progression-free survival of 4.4 months.

Witzig et al. focused on Lenalidomide 25 mg in monotherapy in relapsed/refractory B-cell lymphomas. The cohort of patients was 217, 19 of them had a stage III FL. Regarding this patients subset, ORR was 42%, CR/Cru was 11%, median PFS was 8.9 months, median duration of response was not reached.

The cytotoxic effect of Rituximab appears to involve CDC, ADCC and induction of apoptosis. Early studies of Lenalidomide show the potential for high CR rates and long duration of response in FL and Chronic lymphocytic leukemia (CLL). Recent data suggest that the modulation of effector cells by Lenalidomide can enhance the antitumor activity of Rituximab and partially overcome its resistance in cell lines of relapsed/refractory NHL. Lenalidomide appears in fact to greatly enhance the monocyte and NK-mediated ADCC exerted by Rituximab, resulting in an increase of cancer cell killing compared to the single drugs. A synergistic activity between Rituximab and Lenalidomide has been reported in vitro in lymphoma cells and in animal models. Rituximab-lenalidomide (R2) combination has been consequently tested in clinical trials, including untreated or relapsed/refractory indolent NHL, with encouraging results.

The first report about the R2 combination in FL was presented at the 51th ASH meeting by Dutia M et al. Sixteen patients with relapsed/refractory indolent NHL have been treated with R2 combination, obtaining a 75% overall response (ORR) rate with an acceptable toxicity; interestingly, efficacy data seem better in FL patients with a 88% ORR. Moreover, in the unfavourable subgroups of rituximab refractory and heavily pre-treated patients, ORR rates were 57% and 70%, respectively. Estimated progression-free survival for all patients is 12 months. The major limitation of the study was the small number of patients, with only 9 FL patient included in the study.

Twenty-four patients with indolent B-cell lymphoma, previously resistant to Rituximab, received a Rituximab-Lenalidomide +/- Dexamethasone combination until progression of disease or unacceptable toxicity; Lenalidomide was administered at the dosage of 10 mg, 28 days per course. 28 over 45 patients had FL. No further FL group analysis were reported, but the study allowed to assess that also patients resistant to Rituximab in mono-therapy can benefit from R2, with or without Dexamethasone, achieving higher ORR (~61%) with relatively durable responses.

One hundred patients with stage III-IV untreated indolent NHL received the R2 combination in cycles of 28 days (Lenalidomide 20 mg orally once a day from day 1 to day 21 and Rituximab 375 mg/m2 intravenously on day 1). 49 patients (49%) composed the FL subset.

The outcome of FL patients was extremely positive, considering the ORR (98%) and the CR/CRu (85%). Moreover, when the R2 treatment was prolonged after 6 courses, a significant improvement was seen for CR/CRu. Finally, the PFS was 83% for FL patients after 24 months, and the toxicity profile was acceptable.

In CALGB 50401 randomized study 89 recurrent FL patients were treated with Lenalidomide alone versus R2 combination. ORR were 49% vs 75% and EFS was 1.2 vs 2.0 with a median follow up of 1.5 years.

Basing on these promising data, other trials proposed the combination of Lenalidomide and R-CHOP (R2-CHOP), as R-CHOP is the standard treatment for most patients with B-cell lymphomas. Briefly, both Phase I and Phase I/II trials confirmed the potential of the novel combination, although a large multi-centre trial is required to confirm the results.