The SOUNDTRACK F1 study is a phase III randomised open-label trial comparing a CD19/CD3 bispecific antibody, surovatamig, in combination with rituximab in patients with previously untreated follicular lymphoma. The randomised component is randomisation between chemoimmunotherapy and surovatamig plus rituximab but I was presenting the safety run-in of the first 43 patients at this congress.
What was the study design?
For the safety run-in part there was a randomisation to two different dose levels of surovatamig, 2.4mg and 7.2mg. Patients received lead-in dosing with rituximab followed by combination dosing with surovatamig and rituximab for seven cycles and then patients who responded were then able to receive a further seven months of surovatamig maintenance therapy every four weeks.
What were the key results?
The results were encouraging. So the response rate was 95% in the patients at the 7.2mg arm which was declared the recommended phase II dose. It was similarly high but not quite so high in the 2.4mg dose. At this stage the responses appear to be encouraging with progression free survival maintained at 100% in the 7.2mg cohort with no progression events so far. We were also able to demonstrate MRD negativity in 100% of patients at the 7.2mg dose and 90% of patients at the 2.4mg dose, thus explaining why 7.2mg was selected to take forward into phase III.
In terms of safety, the main signals were cytokine release syndrome seen in about 18% or 19% of patients in the two arms respectively, with infections the next most commonly seen adverse event but these were mostly low grade.
What could be the clinical significance of these results?
The clinical significance really pertains to the randomised phase III portion of the study which is a 1:1:1 randomisation to two surovatamig dosing strategies, one with the maintenance and one without, compared with chemoimmunotherapy. The primary endpoint of that is going to be progression free survival with a coprimary endpoint of overall response rate. That study is ongoing and so we look forward to seeing the primary analysis at a future scientific congress.
