Combination chemotherapy followed by an immunotoxin (anti-B4-blocked ricin) in patients with indolent lymphoma: results of a phase II study.

The purpose of this article was to evaluate the antitumor effects of a combination chemotherapy program based on ProMACE (prednisone, methotrexate, doxorubicin [Adriamycin], cyclophosphamide, etoposide) followed by a B cell-specific immunotoxin in the treatment of patients with advanced-stage indolent histology non-Hodgkin's lymphomas. We performed a prospective phase II clinical trial in a referral-based patient population. After confirmation of diagnosis and staging evaluation, 44 patients (10 small lymphocytic lymphoma, 27 follicular lymphoma, 7 mantle cell lymphoma; 30 without prior therapy, 14 previously treated) received six cycles of ProMACE-CytaBOM (cytarabine, bleomycin, vincristine [Oncovin], mechlorethamine) combination chemotherapy (with etoposide given orally daily for five days) followed by a 7-day continuous infusion of anti-B4-blocked ricin immunotoxin at 30 microg/kg/day given every 14 days for up to six cycles. A complete response was achieved in 25 of 44 patients (57%), 21 from the chemotherapy alone, 3 converted from partial to complete response with the immunotoxin, and 1 patient became a complete responder after a surgical procedure to remove an enlarged spleen that was histologically negative for lymphoma. With a median follow-up of 5 years, 14 of 25 complete responders have relapsed (56%); median remission duration was 2 years, and overall survival was 61%. Forty-two percent of the complete responders have been in continuous remission for more than 4 years. The median number of courses of immunotoxin delivered was two usually because of the development of human anti-ricin antibodies. ProMACE-CytaBOM plus anti-B4-blocked ricin does not produce durable complete remissions in the majority of patients with indolent lymphoma. However, the remissions appear quite durable (> 4 years) in about 40% of the complete responders.