SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) disclosed that its Phase 2 study of the CDK9 inhibitor SLS009 in combination with azacitidine and venetoclax produced clinically meaningful activity in 35 evaluable patients with relapsed or refractory acute myeloid leukemia (AML) featuring myelodysplastic syndrome–related changes (AML‑MR). The overall response rate—defined as complete remission, complete remission with incomplete blood count recovery, or marrow complete remission—was 46%, with 29% achieving CR or CRi. In the subset of patients who had received only one prior line of therapy, the response rate climbed to 58%.
The median overall survival in the least pretreated cohort reached 8.9 months, a dramatic improvement over the historically expected 2.6 months for this high‑risk group. Patients harboring ASXL1 or TP53 mutations also showed encouraging activity, with response rates of 48% and 57% respectively. These figures suggest that SLS009 can overcome venetoclax resistance by suppressing MCL‑1 expression, a key mechanism of BCL‑2 inhibitor failure. The safety profile was favorable; no dose‑limiting toxicities or treatment‑related deaths were reported, and the combination was well tolerated across all cohorts.
SELLAS plans to expand the regimen into newly diagnosed AML patients with high‑risk features in the first quarter of 2026, leveraging the encouraging activity seen in heavily pretreated patients. The company’s leadership highlighted that the data reinforce SLS009’s potential to address an unmet need in a population with limited therapeutic options. The results also position SELLAS to attract partnership or licensing interest, potentially accelerating regulatory submission and commercialization timelines.
Investors reacted strongly to the data, with pre‑market trading on December 8 showing a 4 % lift. Call option activity spiked on December 5, reflecting heightened bullish sentiment ahead of the announcement. The market’s enthusiasm underscores the perceived value of a drug that can extend survival in a difficult‑to‑treat AML cohort and may open new revenue streams for SELLAS.
Dr. Dragan Cicic, Senior Vice President and Chief Development Officer, emphasized that “the combination of SLS009 with azacitidine and venetoclax demonstrates encouraging activity in a heavily pretreated population with adverse‑risk AML‑MR, including those harboring ASXL1 and TP53 mutations.” He added that the data “further reinforce the therapeutic potential of SLS009 to overcome resistance to venetoclax‑based regimens by suppressing the expression of MCL‑1.” The company’s strong financial flexibility, with a current ratio of 8.28, supports continued investment in clinical development and potential partnership negotiations.
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