Efficacy of Yttrium-90 Zevalin Outside of Clinical Trials: Preliminary Results of a Retrospective Bi-Center Study

Background and Aim: Due to limited data regarding the efficacy of Radioimmunotherapy with ⁹⁰Y-Zevalin (RIT-Z) outside of controlled clinical trials, we carried out a biinstitutional, international retrospective study to assess the efficacy of RIT-Z in a routine clinical setting. The relationship between the number of previous therapies and outcomes as well as the response to the last therapy was assessed. Possible differences in outcomes for patients treated in the two different centers were also analyzed.

Materials and Methods: Forty-three consecutive patients treated at the University Hospital of Lausanne (CHUV, Switzerland) and at S. Andrea University Hospital of Rome (Italy) were evaluated, none of which had been previously included in clinical trials. Only 31 patients entered the final analysis: patients lost at follow up, undergoing autologous transplantation (ASCT), or treated within the last 3 months were excluded. Efficacy of therapy was evaluated in terms of Overall Survival (OS), Progression Free Survival (PFS), and Time to Next Treatment (TTNT). Survival curves were obtained with the Kaplan- Meier method (statistical significance = p<0.05).

Results: Characteristics of the patient population are listed in Table 1. Although 50% of the patients had aggressive histologies, patients treated at S. Andrea had slightly more favorable features than those treated at CHUV. Fourteen patients (45%) had received at least 4 previous treatments, and all had received Rituximab. Fourteen patients (45%) had not responded to the last therapy, while 6 (19%), all treated at S.Andrea, were considered disease-free at the time of RIT-Z, which was administered for consolidation. Median follow up time was 20 months (11.5 vs. 25 months for S.Andrea and CHUV, respectively).

Median PFS and TTNT were similar. After achieving a partial response, 2 patients were referred to Rituximab maintenance after RIT-Z and remain progression-free. Median OS was still not attained. Although not statistically significant, a trend towards better outcomes for S. Andrea patients was found. In comparing patients with indolent and aggressive lymphoma, only PFS was found to be significantly different (median PFS: 10 vs. 5 months, p<0.05). In patients with <4 and ≥ 4 previous therapies, twenty month OS was 88% vs. 53.6% (p=0.02), respectively; median TTNT was 22 vs. 5 months (p=0.013), while differences in PFS did not attain statistical significance. The duration of response in non-responders to their last therapy was shorter than in responders: 20-month OS- 44% vs. 94% (p=0.0015), median PFS and TTNT- 3.5 vs. 15 months (p=0.0002) and 4 vs. 15 months (p=0.0001), respectively. Median PFS and TTNT after RIT-Z did not differ from those found after the last therapy. A significant difference in outcomes for heavily pretreated or refractory patients was found in those with low grade follicular lymphoma.

Conclusions: Poorer outcomes were found in our patient population treated in a routine clinical setting compared to those enrolled in clinical trials. This may be related to greater heterogeneity of our study cohort which included more patients with unfavorable conditions (e.g. aggressive NHL, ≥4 treatment courses including rituximab in all, and ASCT in 25%). Our results suggest that the best benefit may be expected with RIT-Z either for consolidation or relatively earlier in the course of NHL treatment.

Table 1.