RESULTS: This interim analysis included 33 pts with intermediate-, high-, and very-high-risk MDS at the data cutoff of 6 months after cycle 1 day 1 of treatment with sabatolimab and an HMA. The median age was 69 years (range, 39-86). At data cutoff, 8 pts were in ongoing treatment, and 25 pts had discontinued the core phase. Reasons for discontinuation included new therapy for study indication (n=6), physician decision (n=6), pt decision (n=5), progressive disease (n=4), unsatisfactory therapeutic effect (n=2), adverse event (AE) (n=1), and death (n=1). Of those who discontinued study treatment, 6 pts were in ongoing evaluation in the extension phase and 3 pts were in ongoing evaluation in the post-treatment follow-up phase. The median duration (range) of exposure was 3.9 (0.92-5.91) months for sabatolimab and 4.2 (1.05-6.08) months for HMAs.
Among 33 pts evaluable for safety, most experienced all-grade and grade ≥3 AEs, AEs requiring additional therapy, and serious AEs (Figure). However, the most frequent (≥10%) grade ≥3 AEs were expected hematologic AEs, including febrile neutropenia (42.4%), anemia (39.4%), neutrophil count decrease (39.4%), and platelet count decrease (36.4%). Nonhematologic grades ≥3 AEs occurring in >1 pt included hypertension (18.2%), pneumonia (9.1%), hypoxia (6.1%), and fall (6.1%). Only 1 pt was reported with encephalopathy leading to treatment discontinuation, which was not attributed to study treatment. One pt had a fatal AE for which the cause was not identified but not thought to be related to study treatment by the investigator.
The best overall response results in up to 6 months of treatment were available for 22 pts. Marrow CR (mCR) with and without hematologic improvement (HI) was reported in 18.2% and 9.1%, respectively. Partial remission (PR) and stable disease (SD) with HI was reported in 4.5%, each. CR + mCR + PR was 31.8% (95% CI, 13.9%-54.9%), CR + PR + HI was 27.3% (95% CI, 10.7%-50.2%), and CR + mCR + PR + HI was 36.4% (95% CI, 17.2%-59.3%).
CONCLUSIONS: This interim analysis of the STIMULUS-MDS US study demonstrated that sabatolimab in combination with an oral, IV, or SC HMA was safe and well tolerated, with AEs consistent with previous reports for pts with MDS treated with HMAs. Response rates for the combination are preliminary, and more information will be provided with longer follow-ups.
