Isatuximab plus Pomalidomide and Dexamethasone in Relapsed/Refractory Multiple Myeloma Patients with Plasmacytomas

This subgroup analysis of the ICARIA-MM study sought to assess the efficacy and safety of treatment with isatuximab (Isa) with pomalidomide-dexamethasone (Pd) compared with treatment with Pd in patients with relapsed/refractory multiple myeloma (RRMM) with preexisting plasmacytomas. In the ICARIA-MM study, 307 patients were randomized to the Isa-Pd arm (154 patients) and the Pd arm (153 patients). Isa was administered intravenously at 10 mg/kg weekly for 4 weeks, and after that, administration occurred every other week.

Patients were checked for plasmacytomas at study entry. Soft-tissue plasmacytomas were present in 24 (7.8%) patients. In the Isa-Pd arm, 14 (9.1%) patients had soft-tissue plasmacytomas, and in the Pd arm, 10 (6.5%) patients did. For these patients, a computed tomography scan and magnetic resonance imaging were done at baseline and repeated every 12 weeks (±1 week). Baseline characteristics were determined for this subgroup. The median age of patients in the Isa-Pd arm was 61 years (range, 36-82 years) versus 64 years (range, 42-71 years) in the Pd arm. The median number of prior regimens before study entry in the Isa-Pd arm was 3.5 (range, 2-13) versus 5.5 (range, 2-6) in the Pd arm. For International Staging System stages, the Isa-Pd arm had 50.0% of patients at stage I, 21.4% of patients at stage II, and 28.6% of patients at stage III. The Pd arm had 10.0% of patients at stage I, 50.0% of patients at stage II, and 40.0% of patients at stage III. In the Isa-Pd arm, 21.4% of patients had high-risk cytogenetics; in the Pd arm, 10% of patients did.

The primary objective of this analysis was to determine the impact of Isa-Pd on progression-free survival (PFS) in patients with RRMM with plasmacytomas. In the Isa-Pd arm, the median PFS was 4.57 months (95% confidence interval [CI], 2.40-not calculable [NC]) versus 1.56 months (95% CI, 0.95-4.47) in the Pd arm. The probability of PFS at 12 months for the Isa-Pd arm was 0.31 (95% CI, 0.10-0.56) versus 0.00 (95% CI, NC-NC) for the Pd arm.

Both overall response rate (ORR) and very good partial response (VGPR) were positively impacted by treatment with Isa-Pd. ORR was 50% (7/14) in the Isa-Pd arm compared with 10% (1/10) in the Pd arm. In the Isa-Pd arm, 21.4% of patients (3/14) achieved VGPR compared with 10% of patients (1/10) in the Pd arm. Two of the 3 patients in the Isa-Pd arm who achieved VGPR (a 57-year-old male with IgG kappa RRMM and a 69-year-old female with IgA lambda RRMM) showed complete remission at cycle 3 and reduction at cycle 4 of the extramedullary lesions, respectively, versus 0 in the Pd arm. The male patient completed 21 cycles of treatment and was still on treatment at the study cutoff date. The female patient completed 11 cycles of treatment before a new soft-tissue mass was detected.

Safety was another important assessment. Grade ≥3 treatment-emergent adverse events occurred in 85.7% of patients (12/14) in the Isa-Pd arm compared with 70.0% of patients (7/10) in the Pd arm. There were no infusion reactions grade ≥3; however, 42.9% of patients in the Isa-Pd arm did experience lower grade infusion reactions.

In summary, for patients with RRMM and plasmacytomas, Isa-Pd treatment prolonged PFS and improved ORR and VGPR compared with Pd treatment, with a manageable safety profile.


Reference

  • Abstract and Poster EP978. EHA 2020. June 12, 2020. Isatuximab plus pomalidomide and dexamethasone in patients with relapsed/refractory multiple myeloma and soft-tissue plasmacytomas: ICARIA-MM subgroup analysis.

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