A Phase I Study of Lenalidomide in Combination with Fludarabine-Rituximab in Previously Untreated CLL/SLL.

Abstract 3426

Poster Board III-314

Lenalidomide is an immunomodulatory drug recently reported to have an objective response rate (ORR) of 35-53% in relapsed/refractory CLL, even with poor risk features. Initial therapy of CLL currently includes chemoimmunotherapy combinations like FCR, which have high response rates and improved PFS, but at the cost of myelosuppression and infection. Given the high ORR reported with lenalidomide and its potential to spare immune function, we undertook this Phase I study to explore the safety and tolerability of lenalidomide in combination with fludarabine and rituximab. Eligibility criteria included a confirmed diagnosis of CLL/SLL, previously untreated with systemic therapy with an indication for therapy by NCI-WG 1996 criteria; ANC > 1000, platelets > 50K, and adequate organ function. Six dose levels were planned, beginning with fludarabine 25 mg/m² days 1-3, rituximab 375 mg/m² day 1, and lenalidomide 2.5 mg administered on days 1-21 of a 28-day cycle. The study used a standard 3+3 dose escalation design, with dose limiting toxicity (DLT) assessed in the first 28 days and defined as grade 3 or greater non-hematologic toxicity, grade 4 neutropenia or thrombocytopenia, grade 3 febrile neutropenia, or a >2-week delay in initiating the second cycle. Nine patients were enrolled on this study, 7 males and 2 females, with a median age of 59 yrs (range 37-66). The median time from diagnosis to study entry was 66.1 months (range 11.7-82.8 months). The median WBC at study entry was 99.6 (range 11.1-325.7). Six patients had Rai 3-4 disease, and three patients had bulky lymphadenopathy (>5 cm) on physical exam. Median beta-2 microglobulin level at study entry was 3.8 mg/L (range 2.5-7.7). The first cohort enrolled four patients, of whom two developed DLTs (grade 4 neutropenia persisting through day 50; febrile syndrome with grade 3 rash, myalgias and grade 4 CPK elevation). The study then proceeded to enroll five patients at dose level -1, with the same dosing of rituximab and fludarabine, but reduced lenalidomide dosing of 2.5 mg every other day for 21 of 28 days. Only two of five patients on dose level -1 completed the planned six cycles of therapy. The other three patients discontinued after 3 cycles due to toxicity: persistent grade 2 thrombocytopenia preventing further therapy; recurrent grade 3-4 neutropenia and thrombocytopenia, despite growth factor support, dose reduction and holding lenalidomide; and intermittent recurrent grade 3 tumor flare, rash and hand-foot syndrome, along with recurrent grade 3 neutropenia despite similar measures as above. At that point the study was closed to enrollment due to the significant myelotoxicity and idiosyncratic tumor flare, resulting in only two of nine patients completing the planned therapy. The median number of cycles completed for all patients was three. Six of the nine enrolled patients were evaluable for response, with five of nine having objective responses (56%, 90% CI 25-83%). No significant difference was observed in IgG and IgM levels between baseline and two months on study, although a trend toward a decrease in IgA levels (p=0.05) was observed. Baseline CD4 counts were variable (median 1139, range 529-2687), but showed significant declines of 574 cells by week 4 (p=0.003) and 707 cells by post-treatment (p=0.002). Analysis of alterations in serum cytokines is ongoing. We conclude that administering lenalidomide concurrently with fludarabine and rituximab is difficult, does not appear to preserve immune function, and limits the ability to deliver adequate therapy with either drug. Other trials currently in progress are exploring alternative schedules of lenalidomide administration with fludarabine and other standard CLL chemotherapy regimens; our data would favor a sequential schedule.