Single-agent fludarabine therapy showed higher response and longer survival in B-CLL patients with untreated or relapsed disease, as compared with anthracycline-based regimens [26, 27]. Furthermore, fludarabine in combination with cyclophosphamide (FC) was the most effective regimen, although CR was achieved in only 23–38% of patients [28–30]. Since the combination of rituximab with fludarabine showed a synergistic effect in substantial preclinical studies [67], the addition of rituximab to a fludarabine-containing regimen (F or FC) was investigated.

The treatment outcome of rituximab combined with fludarabine was evaluated in a phase II trial of GCLLSG [83]. Thirty-one previously untreated or relapsed B-CLL patients received fludarabine at standard doses (25 mg/m² per day, days 1–5, 29–33, 57–61, and 85–89) and rituximab (375 mg/m², days 57, 85, 113, and 151). ORR and CRR were 87% and 32%, respectively. Toxicity of FR regimen was manageable with grade 3 or 4 neutropenia in 42% and severe infections in 13% of patients. In a randomized phase II trial, the CALGB 9712 trial, fludarabine with concurrent rituximab was compared to sequential rituximab in previously untreated B-CLL patients [31]. Patients received six courses of fludarabine with or without rituximab, followed by four weekly administrations of rituximab. Among a total of 104 patients, those receiving concurrent regimen obtained a higher response rate (ORR and CRR; 90% and 47% in concurrent arm and 77% and 28% in sequential arm, respectively) with increased grade 3 or 4 neutropenia (74% vs. 41%). In a retrospective comparative analysis of CALGB 9712 and CALGB 9011 trial, 104 patients of the CALGB 9712 protocol treated with FR were compared to 178 patients of the CALGB 9011 protocol treated with single-agent fludarabine (F) [32]. The patients receiving FR had a significantly better PFS (P < 0.0001) and overall survival (OS) (P = 0.0006) than patients receiving fludarabine alone. The 2-year PFS was estimated at 67% in the FR arm and 45% in the F arm, and the 2-year OS was estimated at 93% and 81% in the FR and F arms, respectively. The incidence of infections was similar between the treatment arms. These results demonstrate that FR is a potent and feasible treatment option for B-CLL patients.

Chemoimmunotherapy with FCR is currently recognized as the standard treatment for physically fit young patients with untreated B-CLL (Fig. 6.1). In a phase II trial conducted at the MD Anderson Cancer Center (MDACC), 300 patients with previously untreated B-CLL were enrolled and received FCR [35, 84]. ORR was achieved in 95%, CR in 72%, nodular PR (nPR) in 10%, PR due to cytopenia in 7%, and PR due to residual disease in 6% of patients. With a median follow-up of 6 years, the 6-year overall and failure-free survivals were 77% and 51%, respectively. The median time to progression (TTP) was 80 months.

These results were superior to a historical control receiving previous generations of B-CLL therapy and led to the large randomized CLL8 trial by GCLLSG, which compared outcomes of FCR to those of FC as a first-line treatment for B-CLL patients (Table 6.1) [33, 85]. In CLL8, 817 physically fit patients with untreated B-CLL were randomly assigned to receive six courses of FC (intravenous fludarabine (25 mg/m² per day) and cyclophosphamide (250 mg/m² per day) for the first 3 days of each 28-day treatment course) with or without rituximab (375 mg/m² on day 0 of the first course and 500 mg/m² on day 1 of the second to sixth courses). The FCR arm obtained a significantly higher ORR than the FC arm (90% vs. 80%, p < 0.001) with a significantly higher CRR (44% vs. 22%, p > 0.001) and improved survival. With a median follow-up of 5.9 years, the median PFS were 56.8 and 32.9 months for the FCR and FC arms (HR = 0.59, 95% CI 0.50–0.69, P < 0.001), respectively, and the median OS was not reached for the FCR arm and was 86.0 months for the FC arm (HR = 0.68, 95% CI 0.54–0.89, P = 0.001). In the analysis of prognostic factors including molecular cytogenetics, the improved survival benefit with FCR was applied for most prognostic subgroups including 11q deletion, although FCR did not improve the survival of patients with del17p. Furthermore, in a subgroup of patients with a mutated IGHV status, patients who were treated with FCR had a significant longer survival than those treated with FC. Median PFS was not reached for the FCR arm and was 41.9 months for the FC arm (HR 0.47, 95% CI 0.33–0.68, P = 0.001). The 5-year OS after FCR and FC were 86.3% and 79.8%, respectively. The Kaplan-Meier PFS curve appeared to plateau, and these findings might suggest a curative treatment with FCR for these particular B-CLL patients. In the safety analysis, neutropenia occurred more frequently in FCR arms (grades 3–4, FCR 34%, FC 21%), while other adverse events including infection, anemia, and thrombocytopenia were similar. Moreover, there was no significant difference in secondary malignancies including Richter’s transformation between FCR arms (13.1%) and FC arms (17.4%) (p = 0.1).

Similar results were shown in a phase III trial comparing FCR with FC in patients with previously treated B-CLL [34]. Five hundred and fifty-two patients with no prior administration of rituximab were enrolled and randomly assigned to FCR or FC treatment arm. FCR significantly improved PFS (HR 0.65, P < 0.001; median, 30.6 months for FCR vs. 20.6 months for FC), ORR (69.9% vs. 58.0%, p = 0.0034), and CRR (24.3% vs. 14.0%, P < 0.001). The rate of grade 3 or 4 adverse events including neutropenia and serious adverse events was higher in the FCR arm compared to the FC arm, although the incidence of infections did not differ between the treatment arms, and FCR was well tolerated. These findings led to the establishment of rituximab in B-CLL treatment, and the FCR regimen was recognized as a standard regimen for physically fit patients with untreated B-CLL.

Consequently, the hypothesis that a more intensive chemotherapy might increase the therapeutic effect of FCR regimen was investigated. The addition of other agents to FCR regimen, such as mitoxantrone [37, 86], lenalidomide [87], or alemtuzumab [88], demonstrated encouraging clinical activity in previously untreated B-CLL, with an ORR of 92–100% and a CRR of 58–82%. While these more intensive chemotherapy regimens showed remarkable efficacy, there was a considerable increase in the incidence of adverse events, especially infections, in most of these trials. Despite showing substantial efficacy, these more intensive regimens have not been evaluated by a randomized comparison to the FCR regimen and thus have not become the standard regimen for untreated B-CLL patients.

However, it is important to note that B-CLL patients are mostly elderly, and the FCR regimen was often too toxic and therefore not applicable to these patients. Therefore, modified FCR regimens of lower intensity were investigated to maintain the efficacy but reduce the adverse events, especially neutropenia and infections.

Two modified FCR regimens with reduced fludarabine and cyclophosphamide dosages and increased rituximab frequency were examined in phase II trials [89–91]. One trial demonstrated favorable outcome and reduced toxicity compared to the previous trials with FCR, although the median age of patients in this trial was only 58 years [89, 90]. Another trial focused on patients over 65 years old and demonstrated high efficacy, although myelosuppression was severe and frequent dose adjustments were required [91]. Therefore, these trial results could not be generalized to unfit or frail elderly B-CLL patients.

Another alternative attempt to reduce the toxicity of FCR regimen was to substitute fludarabine (and cyclophosphamide) with other purine analogs (cladribine, pentostatin, or bendamustine). The combination of cladribine [92] or pentostatin [93, 94] and rituximab with or without cyclophosphamide seemed to be inferior to FCR regimen or could not demonstrate a lower toxicity compared to FCR regimen. Therefore, these are not considered as a standard treatment for physically fit patients with B-CLL, and the value of these regimens remains to be elucidated.

Bendamustine has structural similarities to both alkylating agents and purine analogs and had considerable activity for indolent B-cell malignancies including B-CLL [95–97]. Bendamustine produced significantly greater efficacy but more frequent neutropenia and infection than chlorambucil in previously untreated B-CLL patients and therefore did not show a benefit in OS [98, 99]. In a small phase I/II trial, single-agent bendamustine yielded an ORR of 56% in relapsed/refractory B-CLL patients [100]. Based on these results, BR regimen was conducted for relapsed/refractory and previously untreated B-CLL patients and showed promising outcomes.

In a phase II trial of 78 relapsed/refractory B-CLL patients where most had previously received a fludarabine-containing regimen, patients received bendamustine 70 mg/m² per day on days 1 and 2 and rituximab 375 mg/m² on day 0 for the first course and 500 mg/m² on day 1 for subsequent courses every 28 days for up to six courses [101]. Based on intent-to-treat analysis, ORR and CRR were achieved in 59.0% and 9.0% of patients, respectively. ORR was 45.5% in fludarabine-refractory patients and 60.5% in fludarabine-sensitive patients. With a median follow-up of 24 months, the median event-free survival (EFS) was 14.7 months. The incidence of grade 3 or 4 severe infections, neutropenia, thrombocytopenia, and anemia were 12.8%, 23.1%, 28.2%, and 16.6%, respectively. In genetic analyses, patients with del17p did not respond to BR regimen, similar to other purine analogs.

BR regimen was also investigated in previously untreated B-CLL patients [102]. The dose and schedule of BR regimen were essentially as described above, but the dose of bendamustine was increased to 90 mg/m² per day. Out of 117 patients, ORR and CRR were 88.0% and 23.1%, respectively. With a median follow-up time of 27.0 months, median EFS was 33.9 months, and 90.5% of patients were alive. Grade 3 or 4 infections, neutropenia, thrombocytopenia, and anemia were documented in 7.7%, 19.7%, 22.2%, and 19.7% of patients, respectively. In a genetic analysis, BR had modest activity for patients with del17p, as for relapsed/refractory patients. In comparison to FCR regimen, BR appeared to show similar efficacy, with a lower incidence of severe infections and neutropenia.

From promising results, a phase III trial, CLL10 trial of the GCLLSG, comparing the BR regimen with FCR regimen for previously untreated B-CLL in physically fit patients without del17p was conducted (Table 6.1) [103, 104]. A total of 564 patients with CIRS score ≤6 and creatinine clearance >70 ml/min and without del17p were enrolled, and these patients received up to six courses of BR or FCR. Patient background was well balanced between the two arms excluding age (22% in BR vs. 14% in FCR, aged >70 years, p = 0.020) and the proportion of unmutated IGHV status (68% in BR vs. 55% in FCR, P = 0.003). The ORR was 97.8% in both arms, although BR was inferior to FCR in CRR (31.5% vs. 40.7%, P = 0.026), in MRD negativity in peripheral blood (62.9% vs. 74.1%, P = 0.0024), in MRD negativity in the bone marrow (31.6% vs. 58.1%, P < 0.001), and in the median PFS (43.2 vs. 53.7 months, HR = 1.589, 95% CI 1.25–2.079, P = 0.001) with a median follow-up time of 35.9 months. In particular, physically fit patients (CIRS ≤3, only one CIRS item, age <65 years) benefited the most from FCR. However, there was no statistical difference in PFS between both arms in patients ≥65 years, CIRS 4–6 or >1 CIRS item. The 3-year OS was 92.2% in the BR arm and 90.6% in the FCR arm, with no significant difference (HR = 1.030, 95% CI 0.618–1.717, p = 0.910). In safety analysis, grade 3 or 4 severe neutropenia and infections were more frequently documented in the FCR arm (87.7% vs. 67.8%, p < 0.001, and 39.8% vs. 25.4%, p = 0.001), especially in elderly patients >70 years (48.4% vs. 26.8%, p = 0.001). The incidence of anemia and thrombocytopenia was not significantly different (14.2% vs. 12.0%, p = 0.46, and 22.4% vs. 16.5%, p = 0.096). Treatment-related mortality also did not differ significantly between both treatment arms (3.9% in FCR and 2.1% in BR). Based on these results, FCR regimen remains the standard therapy in physically fit young patients. The BR regimen can be an alternative regimen in elderly fit patients, as the FCR regimen more frequently causes severe neutropenia and infection in these patients (Fig. 6.1).

Chlorambucil is a nitrogen mustard alkylating agent and has been considered the standard treatment of B-CLL for several decades, especially in elderly patients with relevant comorbidities, since chlorambucil offers a modest response rate, but low toxicity and the convenience of oral intake [25]. In the past, several more potent and promising agents, including fludarabine, bendamustine, and alemtuzumab, had not demonstrated any survival benefit compared to chlorambucil [42, 98, 99, 105–107]. The addition of rituximab to chemotherapy had increased the efficacy of B-CLL chemotherapy regimens under evaluation, and the addition of rituximab to chlorambucil (R-CLB) showed similarly encouraging results in some phase II trials [108, 109]. In these phase II trials, R-CLB was well tolerated and of benefit. These compared favorably with published results for chlorambucil monotherapy and subsequently led to the CLL11 phase III trial (Table 6.1) [110, 111]. The CLL11 trial by GCLLSG evaluated the efficacy of rituximab or obinutuzumab in combination with chlorambucil (R-CLB or G-CLB) in comparison to chlorambucil alone in patients with previously untreated B-CLL and relevant comorbidities. In this trial, R-CLB showed a survival benefit compared to chlorambucil monotherapy (the details are described below). Taken together, R-CLB has become one of the current standard treatments for physically unfit B-CLL patients.