Rituximab dose-escalation trial in chronic lymphocytic leukemia

To conduct a dose-escalation trial of rituximab in patients with chronic lymphocytic leukemia (CLL) to define the maximum-tolerated dose (MTD), to evaluate first-dose reactions in patients with high circulating lymphocyte counts, and to assess the efficacy at higher versus lower doses.

Fifty patients with CLL (n = 40) or other mature B-cell lymphoid leukemias (n = 10) were treated with four weekly infusions of rituximab. The first dose was 375 mg/m(2) for all patients; dose- escalation began with dose 2 but was held constant for each patient. Escalated doses were from 500 to 2,250 mg/m(2).

Toxicity with the first dose (375 mg/m(2)) was noted in 94% of patients but was grade 1 or 2 in most, predominantly fever and chills. Six patients (12%) experienced severe toxicity with the first dose, including fever, chills, dyspnea, and hypoxia in all six patients, hypotension in five, and hypertension in one. Toxicity on subsequent doses was minimal until a dose of 2,250 mg/m(2) was achieved. Eight (67%) of 12 patients had grade 2 toxicity, including fever, chills, nausea, and malaise, although no patient had grade 3 or 4 toxicity. Severe toxicity with the first dose was significantly more common in patients with other B-cell leukemias, occurring in five (50%) of 10 patients versus one (2%) of 40 patients with CLL (P <.001). The overall response rate was 40%; all responses in patients with CLL were partial remissions. Response rates were 36% in CLL and 60% in other B-cell lymphoid leukemias. Response was correlated with dose: 22% for patients treated at 500 to 825 mg/m(2), 43% for those treated at 1,000 to 1,500 mg/m(2), and 75% for those treated at the highest dose of 2,250 mg/m(2) (P =.007). The median time to disease progression was 8 months. Myelosuppression and infections were uncommon.

Rituximab has significant activity in patients with CLL at the higher dose levels. Severe first-dose reactions were uncommon in patients with CLL, even with high circulating lymphocyte counts, but were frequent in patients with other mature B-cell leukemias in which CD20 surface expression is increased. Efficacy of rituximab was also significant in this group of patients.