Transplant with radioimmunotherapy (RIT)-based conditioning is a viable treatment option for patients with indolent—but not aggressive—B-cell non-Hodgkin lymphomas (NHLs), according to researchers.

Long-term follow-up data showed “excellent” outcomes in patients with indolent B-NHL who received conditioning with ⁹⁰Y-ibritumomab tiuxetan plus fludarabine and low-dose total body irradiation (TBI) prior to HLA-matched hematopoietic stem cell transplant (HSCT).

However, long-term outcomes were inferior in patients with diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL).

Camille E. Puronen, MD, of the University of Washington in Seattle, and her colleagues reported these results in Biology of Blood and Marrow Transplantation.

The study enrolled 40 patients with high-risk B-NHL. This included DLBCL (n=14), chronic lymphocytic leukemia (CLL; n=10), MCL (n=8), follicular lymphoma (FL; n=6); hairy cell leukemia (HCL; n=1), and marginal zone lymphoma (MZL; n=1).

Patients were treated with 0.4 mCi/kg ⁹⁰Y-ibritumomab tiuxetan, given 2 weeks prior to HSCT, to a maximum dose of 32 mCi.

Patients also received fludarabine at 30 mg/m² on day 5, 6, and 7 prior to HSCT and 2 Gy TBI given on the day of transplant.

In an earlier report, the objective response rate (ORR) was 60%, and 35% of patients had a complete response (CR) or unconfirmed CR.

The researchers said early responses were not associated with disease bulk or chemoresistance, as the ORR was 59% in patients with bulky or chemoresistant disease.

However, responses were associated with histology, as the ORR was 38% in patients with DLBCL, 50% in those with MCL, 83% in those with FL, and 90% in those with CLL.

Long-term survival

In the current report, 11 of 40 patients were still alive at a median follow up of 9 years (range, 5.3 to 10.2). Fourteen patients died of disease progression, and 14 died from complications of HSCT.

The 5-year overall survival (OS) was 40%, and the 5-year progression-free survival (PFS) was 28%.

The best survival rates were in patients with indolent histology. The 5-year PFS was 44% in these patients, and the 5-year OS was 67%.

The researchers said early CR was not associated with long-term survival. However, patients who had at least stable disease (SD) at earlier time points did have the opportunity to achieve long-term survival. All patients who progressed before day 84 were dead by the 1-year mark.

Of the 11 patients who were still alive at a median follow up of 9 years, 4 had a CR or unconfirmed CR at day 84 (FL: 1; CLL: 2; MCL: 1); 6 were in partial response (CLL: 3; FL: 1; MCL: 1; MZL: 1); and 1 patient with FL had SD.

Among the 18 patients with indolent NHL, long-term PFS was observed in 5 of the 7 patients who achieved early CR and 8 of the 11 patients who did not achieve early CR.

Two of the 4 MCL patients who achieved an early CR had long-term PFS, but none of the MCL patients without an early CR had long-term PFS.

Among DLBCL patients, 1 of the 4 who achieved early CR had long-term PFS, but none of the patients without an early CR had long-term PFS. Only 1 DLBCL patient survived beyond 5 years. None survived beyond 8 years.

The researchers said the favorable outcomes in patients with indolent B-NHL are consistent with the known efficacy of RIT and the graft-versus-leukemia effect in these patients.

The team also noted that, since this trial began, several novel agents have been approved for the treatment of indolent B-NHL, which means allogeneic HSCT is often moved to later in the disease course.

The researchers concluded that ⁹⁰Y-ibritumomab tiuxetan-based conditioning could “continue to play an important role in these settings,” but “improved strategies are needed” for patients with MCL and DLBCL.

Transplant strategy not viable for aggressive B-NHL