Long-term follow-up of a phase I/II trial of radioimmunotherapy (RIT) with yttrium 90 (90Y) ibritumomab tiuxetan for CD20+ B-cell non-Hodgkin's lymphoma (NHL)

Abstract

6574 Background: Updated time to disease progression (TTP) and duration of response (DR) are reported for responders from a multicenter phase I/II dose-escalation trial of 90Y ibritumomab tiuxetan (Zevalin®) in 51 patients (pts) with relapsed or refractory CD20+ B-cell NHL. Methods: 5 pts were treated at a dose of 0.2 mCi/kg, 15 at 0.3 mCi/kg, and 30 at 0.4 mCi/kg; 1 pt was not treated. Maximum tolerated dose (MTD) was 0.4 mCi/kg for pts with baseline platelets (plts) ≥ 150,000/μL (0.3 mCi/kg for plts 100,000–149,000/μL). Maximum dose for all pts was 32 mCi. Median age was 60 years (yrs) (range, 24–82). Median time from diagnosis to treatment was 3.8 yrs (range, 0.7–33.1). Median number of prior chemotherapy regimens was 2 (range, 1–7); 47 pts (92%) had received an anthracycline. 10 pts (20%) were resistant to prior chemotherapy. At study entry, 59% of pts had ≥ 1 tumor mass ≥ 5 cm; 43% had bone marrow involvement. Results: TTP and DR in responders were updated, response rates (RR) reported at all dose levels by International Workshop Response Criteria. Complete response (CR), CR unconfirmed (CRu), and partial response (PR) rates were 29%, 22%, and 22%, respectively, for an overall RR (ORR) of 73% (51% CR/CRu). ORR in pts with follicular lymphoma (FL) was 85% (58% CR/CRu, 27% PR). TTP and DR in all responders were 12.6 months (mos) and 11.7 mos, respectively. At MTD, TTP and DR in complete responders (CR/CRu) were 28.3 and 27.5 mos, respectively. 9 pts (24% of responders) had TTP >3 yrs; 5 had FL and 4 had diffuse large cell lymphoma (DLCL). 5 pts (FL, 3; DLCL, 2) are still in CR (range, 60+-74+ mos). Conclusions: 90Y ibritumomab tiuxetan produces high RRs and durable responses in pts with relapsed or refractory B-cell NHL. Durable responses >5 years have been seen in FL and DLCL. Because most relapses in DLCL occur early, the 2 DLCL pts with durable remissions might be cured. This observation provides the basis for further studies to define the efficacy of 90Y ibritumomab tiuxetan in relapsed DLCL. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Biogen/IDEC Biogen/IDEC Biogen/IDEC Biogen/IDEC