Abstract
BACKGROUND: We have previously studied and reported that the combination of pentostatin (P, 2 mg/m2), cyclophosphamide (C 600 mg/m2) and rituximab (R 375 mg/m2) in previously untreated CLL is highly effective with an overall response (OR) rate of over 90% and a complete response rate (CR) of 41% (Blood109:405–411, 2007). We also found that this regimen can be effective even in older patients (>70 y), those with elevated beta-2 microglobulin levels, and patients with mildly reduced creatinine clearances (Cancer. 109:2291–2298, 2007). To determine whether similar benefit could be achieved without inclusion of an alkylating agent, we conducted a follow-up trial testing pentostatin and rituximab without cyclophosphamide and employing a higher pentostatin dose (4 mg/m2).
METHODS: Eligible pts had documentation of active CLL by standard NCI-WG criteria, and were previously untreated. Treatment schema consisted of 6 cycles of pentostatin (4 mg/m2) and rituximab given every 21 days. Pentostatin was given on the first day of each cycle following infusion of rituximab. Rituximab was given at 100mg/m2 IV at day 1, then 375 mg/m2 IV on days 3 and 5 of the first treatment cycle. During cycles 2 to 6, Rituximab was given at 375 mg/m2 as a single IV infusion day 1 of week 4, 7, 10, 13 and 16. All patients were staged two months after completion of the 6 cycles of PR using the NCI-WG criteria.
PATIENT CHARACTERISTICS: Overall, 33 patients were enrolled at Mayo Clinic and Ohio State University between July 2005 and February 2008. All 33 were eligible: 82% male, median age 65 (range: 45–81), with 9 (27%) being 70 years or older. 76% had a baseline ECOG PS of 0, and the rest were ECOG PS 1. Overall, 36% of patients had intermediate Rai risk (stage I–II) and 63% high Rai risk (stage 3–4) disease. Prognostic testing revealed that 36% were CD38+, 50% were Zap-70 +, and 39% had an unmutated IgVh status. Chromosome analysis by FISH found that 99% had detectable FISH panel defect, including 61%, 27% and 3% of patients with 1, 2, or 3 FISH detects, respectively.
RESULTS: 28 of 33 patients (85%) completed therapy. While on treatment, 6 pts (18%) had a dose held or modified with 4 of these delays due to hematologic AE. For adverse events deemed at least possibly related to treatment, 4 (12%) pts experienced grade 3+ hematologic toxicity and 5 (15%) experienced grade 3+ non-hematologic toxicity. Out of all 33 enrolled patients, the overall response rate was 79% with 10 CR, 6 nPR, and 10 PR. At the time of this analysis, 29/33 patients are still alive with a median follow-up time of 14 months on surviving patients. To date 17/33 (52%) of patients have progressed with an estimated median time to progression of 12 months (95% CI: 8.5–21 months). 13/26 responders have progressed. Median duration of response is 12.5 months ((95% CI: 11–21 months).
Finally, since eligibility were nearly identical and enrollment accrued at the same two academic centers, we compared the patient characteristics, response rates, and PFS of the 33 patients treated with PR to the 64 patients previously treated on our PCR trial. Patients in the two studies were generally similar with respect to demographic and prognostic characteristics, although patients in the PR trial had higher WBC and were less likely to be IgVH unmutated (Table). Although the differences in ORR and CR rate were not significantly different, the PFS appeared to be inferior in patients treated with PR as compared to PCR (12 months vs. 31 months; p=0.003).
CONCLUSION: Although the PR regimen achieves a high OR response rate, the PFS appears inferior to PCR therapy. These findings suggest that increasing the purine nucleoside analogue dose does not eliminate the need to include cyclophosphamide in chemoimmunotherapy for patients with CLL.
PCR Trial N=64 PR Trial N=33 P value Age, median(range) 63 years (38–80) 65 years (45–81) 0.34 ≥70 years(%) 28% 27% Male 77% 82% 0.61 Rai stage 0 5% 0 0.46 Rai stage I–II 42% 36% Rai stage III–IV 53% 64% White Cell Count, median(range) 79 × 109/L (11–519) 127 × 109/L (8–430) 0.04 <50 × 109/L 36% 28% 50–149 × 109/L 44% 25% >150 × 109/L 20% 47% Serum B2-microglobulin, median(range) 3.97 (1.8–13.5) 3.80 (2.0–8.2) 0.81 >2 × Upper Limit Normal(%) 57% 58% CD38 Positive 34% 36% 1.00 ZAP-70 Positive 36% 50% 0.26 IgVH Unmutated 71% 39% 0.004 FISH Normal, 11% 9% 13q- 35% 42% +12 21% 24% 6q- 2% 0 11q- 22% 18% 17p- 6% 3% other 3% 3% Overall Response Rate 91% 79% 0.12 Complete Response Rate 41% 30% 0.38 Median PFS 31 months 12 months 0.003