Tositumomab and I 131 Tositumomab Achieves Complete Remissions Lasting > 10 Years In Patients with Chemotherapy-Refractory Low-Grade and Transformed B-Cell Lymphomas

The efficacy and safety of tositumomab and iodine I 131 tositumomab (TST/I-131-TST), the Bexxar® Therapeutic Regimen, were evaluated in 60 patients (pts) with chemotherapy-refractory low-grade (LG) or transformed B-cell non-Hodgkin's lymphoma (B-NHL) who had received at least 2 chemotherapy regimens and had either not responded to (72%) or had progressed within 6 months of their last regimen (28%) (J Clin Onc 2001; 19:3918 and Blood 2004; Abstract 2631). The primary efficacy endpoint was comparison of the number of pts who had a longer duration of response to TST/I-131-TST with the number of pts with a longer duration of response to their last qualifying chemotherapy (LQC). Thirty-nine (65%) pts, including 20% who attained a complete response (CR), responded to TST/I-131-TST, compared to 17 (28%) pts, including 3% CR, after their LQC (p<0.001). Seventy-four percent of pts had a longer response duration after TST/I-131TST compared to the LQC. Four pts developed myelodysplasia (MDS), and 5 pts developed human anti-mouse antibodies (HAMA). We report final results of long term follow-up of these 60 pts.

Pts were enrolled from 22 November 1996 to 06 March 1998. Pts alive at the last report date (1 March 2004) were followed for long-term safety and survival, and pts in remission at the last report date were followed for continued response.

Sixty pts received the dosimetric dose, and 58 of 60 pts received both the dosimetric and therapeutic doses of TST/I-131-TST. The median number of prior chemotherapies was 4 (range, 2–13). Fifty-nine of 60 (98%) pts had stage III/IV disease, 56% had bone marrow (BM) involvement, and 88% had ≥ two IPI risk factors at study entry. Thirty-six pts had LG B-NHL, 23 pts had a history of transformed B-NHL, and 1 pt had mantle cell NHL (MCL). Forty-eight (80%) pts have died, of whom 77% died due to lymphoma progression. Twelve pts were alive, and 6 pts were in CR at last follow-up. One pt withdrew consent for further follow-up but was in CR at 5.0 years, and the other 5 pts (4 LG, 1 transformed B-NHL) were in CR of ≥ 10 years' duration. The pts who continued in CR had received a median of 3 different prior chemotherapy regimens (range, 2–5), and no pts had received prior rituximab. For all 12 pts who attained CR, the median duration of response was 9.9 years (range, 0.7–11.7 years). Long-term toxicity included 7 pts who developed hypothyroidism. Secondary cancers included 1 lung adenocarincoma, 1 colon cancer, and 7 skin cancers which were reported previously. In addition, 1 developed a myeloproliferative disorder (MPD). No cases of MDS beyond the 4 previously reported were observed.

A single course of TST/I-131-TST achieved durable remissions in chemotherapy-refractory LG and transformed B-NHL pts, with 5 of the 12 pts who achieved CR still in remission ≥ 10 years later. No additional cases of MDS were observed, but 1 pt developed a MPD since the last report. Thus, the final results of this study demonstrate that TST/I-131-TST is able to attain long-lasting durable CRs, with an acceptable toxicity profile, in a subset of pts with chemotherapy-refractory LG and transformed B-NHL.

Kaminski:GlaxoSmithKline: Patents & Royalties, Research Funding. Zelenetz:GlaxoSmithKline: Research Funding. Press:GlaxoSmithKline: Research Funding; Spectrum Pharmaceuticals: Honoraria; Roche/Genentech: Honoraria. Saleh:GlaxoSmithKline, Novartis, Imcoline, Celgene: Honoraria, Speakers Bureau. Leonard:GlaxoSmithKline: Consultancy. Lister:GlaxoSmithKline: Chairman of Safety Monitoring Board for GSK. Horner:GlaxoSmithKline: Employment. Williams:GlaxoSmithKline: Employment. Lin:GlaxoSmithKline: Consultancy, Employment. Vleisides:GlaxoSmithKline: Employment. Knox:GlaxoSmithKline: Research Funding. Wahl:GlaxoSmithKline: Consultancy, Patents & Royalties; Nihon Medi Physics: Consultancy; Spectrum Pharmaceuticals: Consultancy; Naviscan PET systems: Consultancy; Threshold Pharmaceuticals: Equity Ownership. Vose:GlaxoSmithKline: Research Funding.