Lenalidomide and Rituximab Maintenance Therapy after Front-Line Induction Chemoimmunotherapy in Chronic Lymphocytic Leukemia and Small Lymphocytic Lymphoma

Introduction: Chronic lymphocytic leukemia (CLL) is incurable with standard therapy. With first-line chemotherapy, some patients (pts) may achieve durable remissions of many months/years. Lenalidomide (LEN) has improved progression-free survival (PFS) when given as maintenance (MNT) therapy after front-line chemotherapy (CALGB10404, CLLM1). The combination of LEN + rituximab (LR) has activity in relapsed CLL, hypothesizing benefit as MNT therapy after first-line chemotherapy.

Methods: Adult pts ≥18 years with previously untreated CLL received induction bendamustine (B) 90 mg/m² IV days 1 & 2 and rituximab (R) IV day 1 (375 mg/m² cycle 1, then 500 mg/m² cycles 2-6) for 6 treatment cycles (as few as 4 cycles allowed). MNT therapy with LR was initiated within 12 weeks after cycle 6, day 1 of BR. Criteria to start LR MNT included: neutrophils ≥1000/microliter (uL), platelets ≥75 K/uL, and creatinine clearance ≥40 mL/min. LEN was administered in 28-day cycles for 24 cycles, initially 5-10 mg daily continuous dosing, later modified to 5-10 mg on days 1-21 of each 28-day cycle in 6/2018 due to neutropenia and second malignancy risk. LEN was reduced to 5 mg every other day for toxicities at 5 mg/day. R 375 mg/m2 IV was given every odd cycle (total of 12 doses). Patients discontinuing LEN for any reason were allowed to continue R MNT per protocol. The primary endpoint is PFS with LR MNT therapy, calculated from the first day of MNT therapy until progressive disease (PD), death, or start of a new therapy. Secondary endpoints are response rate and overall survival.

Results: Thirty-four pts have enrolled beginning 11/2013, with follow-up through 6/2019. Median age is 64 years, with 8 pts ≥70 years; 8 women and 26 men. CLL FISH panel is available on all pts: 14 with 13q (as sole abnormality), 9 with 11q deletion, 6 with trisomy 12, 4 with normal FISH panel and 1 with 17p deletion. Heavy chain mutation analysis is available on 11 pts: 8 unmutated, 2 mutated, 1 indeterminate.

Thirty-one pts completed 4 (n=2) or 6 cycles of induction BR; 3 pts are receiving induction BR. Twenty-four pts have received MNT LR; 7 did not receive LR for reasons of PD during induction (n=2), infection (n=1), pt preference (n=2), renal insufficiency (n=1), and new carcinoma (n=1). MNT LR was completed in 7 pts; 9 pts are still receiving LR.

Fourteen subjects have discontinued protocol therapy, 3 during induction due to PD (n=2) and infection (n=1), and 8 during MNT. Toxicities that led to discontinuation of LR were recurrent infections in 7 pts, including 2 events of PJP pneumonia; 4 pts had recurrent neutropenia with infections; 1 pt had neutropenia without infections.

Response is assessable in 31 patients using the International Working Group Consensus Criteria. Best responses to treatment were: partial response 65% (22/34), complete response (CR)/unconfirmed CR 24% (8/34).

The median number of MNT cycles received is 16. The dose intensity of LEN across total cycles received (n=278): 5 mg every other day (52.5%), 5 mg/day (43.9%), and 10 mg/day (3.6%). The most common reason for dose reduction or dose holding was neutropenia.

Most common Gr 3/4 toxicities (reported as events Gr3/Gr4) during MNT therapy were: neutropenia (20/20), leukopenia (19/4), febrile neutropenia (3/1), and infections (11/-). The majority of Gr3 infections were pneumonia/respiratory (n=5). One event of disseminated herpes zoster occurred. Second malignancies during MNT included: basal cell CA (n=1), squamous cell carcinoma (n=5), and colon cancer (n=1). No unexpected second malignancies were observed in pts receiving LR.

Two-year PFS (defined from day 1 of MNT therapy) is 90% (95% confidence interval [CI] 0.78-1), and the median follow-up for 24 patient who started maintenance therapy is 1.79 years (95% CI 1.53-2.7). There have been no deaths.

Conclusion: The combination of LR is effective in sustaining remissions after a BR induction in previously untreated CLL, but with frequent neutropenia and infections even at low doses of LEN. Most patients discontinuing MNT did so due to neutropenia and/or infections. A shorter planned interval of MNT LR (i.e., 6-12 months) may confer similar benefit to extended dosing that is more tolerable. Pts at high risk for short remissions after front-line chemotherapy (e.g., unmutated heavy chain status, 11q deletion and/or failure to achieve minimal residual disease after induction) may be the populations for which LR MNT therapy is most appropriate.