Combination Chemotherapy with Pentostatin, Cyclophosphamide and Rituximab Induces High Rate of Remissions Including Complete Responses and Achievement of Minimal Residual Disease in Previously Untreated B-Chronic Lymphocytic Leukemia.

The nucleoside analogue pentostatin has clinical activity in B-Cell Chronic Lymphocytic Leukemia (CLL) and has shown significant activity and minimal toxicity when combined with cyclophosphamide for previously treated CLL. Building on this, we initiated a trial in 2002 of combined pentostatin (2mg/m²), cyclophosphamide (600 mg/m²) and rituximab (375mg/m²). Of the 33 enrolled eligible patients included in these analyses, seventeen patients were in the high Rai risk group, 25 were male, and median age for this cohort was 62 yrs (range: 40–79); 17 were non-mutated for the immunoglobulin heavy chain variable region gene, and the majority (67%) were CD38 negative. Only 5 patients had no detectable chromosomal abnormalities by FISH at baseline, 20 had a single FISH anomaly, and 8 had 2 or more FISH anomalies. Of all 28 pts with any anomaly, the following specific abnormalities were detected: 13q- (n=17), +12 (n=8), 11q- (n=7), 17p- (n=2), t(14;18) (n=1), 6q- (n=1), and MDM2 (n=1). Of the 33 patients, 22 had grade 3+ toxicity; 16 patients had non-hematologic toxicity wtih the most common symptoms being nausea (6) and vomiting (4). One patient died on study of grade 5 hypoxia as well as hypotension and this was deemed possibly related to treatment. Almost all patients (32/33; 97%) had a best response of PR or better. Including review of bone marrows done 2 months post-treatment, there were 11 CRs (complete response), 7 nPRs (nodal partial response) and 13 PRs. No differences were observed between type of response and mutation status or CD38⁺ status. Post-treatment FISH analyses were available on 27 patients; results for 25 patients became normal after treatment. Of the remaining 2, one patient was 13q- x1 and went from 94% to 27.5% abnormal nuclei after treatment; the other is the patient who died on study. To establish minimal residual disease (MRD) post-response, we used three color flow cytometry to detect CD5⁺/CD19⁺/CD79b⁻ B cells. This approach found all patients had a reduction in CLL B cells with a median reduction of 91% (range: 5 – 100%). Of interest, all 3 response groups (CR vs. nPR vs. PR) had patients with significant reductions in CLL B cells (i.e., >90%). The nPR group was most variable in terms of MRD (median 47%; range: 5–93%) compared to the CR (median: 91%; range: 42–99.9%) and PR (median: 97%; range: 46–100%) groups. In conclusion this novel regimen of pentostatin, cyclophosphamide and rituximab has demonstrated significant clinical activity irrespective of risk stratification parameters with rapid induction of responses, achievement of minimal residual disease in some, and modest toxicity. Patients continue to be accrued to further explore correlative measures of response to treatment.